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. 







A MANUAL 



OF 



STEAM-BOILERS: 



THEIR 



DESIGN, CONSTRUCTION, AND OPERATION. 



FOR TECHNICAL SCHOOLS AND ENGINEERS, 



BY 



m H. THURSTON, M.A., Doc. Eng. ; 



Director of Sibley College, Cornell University; Past President American Society 
of Mechanical Engineers ; Author of a ^^ History of the Steam-engine," 
^ ' ' Materials of Engineering" etc. , etc. , etc. 



- / 



0\^ i "maI; 8 1888 

NEW YORK: 
JOHN WILEY & SONS, 

15 AsTOR Place. 
1888. 






Copyright, 1888, 
By R. H, Thurston. 



^ ^ 33^> 



Drummonb & Net:, 
Electrotypers, 
'-iJ^ 1 to 7 Hague Street. 

. /N jAo ^ Is/ New York. 



PREFACE. 



The following treatise on the steam boiler, its design, con- 
struction, and operation, is the outcome of an attempt to meet 
a demand which has been repeatedly made for a fairly com- 
plete, systematic, and scientific, yet " practical," manual. It 
has been intended to work to a plan that should be sufficiently 
comprehensive to meet the wants of the engineer in his office, 
and yet so rigidly systematic as to be suitable for use as a 
text-book in schools of engineering. It has been the endeavor 
to incorporate the elements of the subject just so far as they 
are needed in preparing the way for the work of the designer, 
the builder, and the manager of steam-boilers ; while also 
amply complete and logical to permit the use of the book in 
the instruction of the student in applied science. It was not 
expected that it would be found practicable to make a manual 
of this kind absolutely complete as a workshop treatise to be 
used by the boiler-maker — a trade rnanual; but it was hoped 
that it might, within these limits, be made fairly satisfactory to 
the engineer engaged in designing. 

The plan of the work is as follows: Beginning with an his- 
torical and descriptive introduction, in which are traced the 
various developments of the apparatus used by the engineers of 
the time of Watt and earlier, and by his successors, and the 
progress made since his time to date, the existing standard 
forms of boiler are described and classified, and their special 
adaptations indicated. A chapter is devoted to the study of 
the characteristics of the materials used by the engineer in the 
construction of steam-generators, and another to the strength 
of these metals in their several forms and compositions, the 
methods of adaptation to the purposes of construction, and to 



IV PREFACE. 

the statement of the precautions to be observed in their intro- 
duction into so important a structure. Another chapter is 
appropriated to the examination of the composition and rela- 
tive values of the various available fuels, and their economical 
use in the production of steam. These chapters on the mate- 
rials and their characteristics are adapted mainly from the 
notes of lectures from which the larger work of the Author — 
'' Materials of Engineering" — was compiled. It has been the 
endeavor of the Author to make this introductory portion of 
the book exceptionally complete, as it is the foundation of all 
that follows, and is a branch of the subject to which much at- 
tention is rarely given in treatises of this character. Follow- 
ing this part of the work are chapters upon the laws of ther- 
modynamics, so far as they find application in the subsequent 
portion of the work, as, for example, in the determination of 
the magnitude of the stock of heat-energy stored in steam, 
and in the calculation of the constants required in tabulation 
of its properties; and this part of the scheme is introductory 
to a study of the properties of water in its several character- 
istic forms, — solid, liquid, gaseous, — and especially of the essen- 
tial attributes of steam at the pressures and temperatures 
which are customarily met with in every-day practice. The 
tables, however, which are here given are carried up to a range 
of pressure and of temperature far exceeding those in common 
use, and it is thought are sufficiently complete to serve their 
purpose for many years, notwithstanding the unintermitted 
progress in the direction of higher pressures which is now ob- 
served, and which is not likely soon to completely cease. In 
these tables the constants of Rankine are adopted, not so 
much because it is considered by the Author, if we may judge 
from what is to-day known on this subject, that they are quite 
as likely to be correct as any others ; but for the reason that 
they have become so generally accepted among engineers, and 
differ so little from the best values taken by earlier authorities, 
that it is probably wisest and safest to retain them — at least 
until the exact quantities are better settled than to-day. It is 
certain that the differences in the magnitudes now taken for 
the heat-equivalent, for example, and between those values 



■ PREFACE. V 

and the exact figures, are too small to be of moment to the en- 
gineer in the daily operations of professional work. Rankine's 
reconstruction of Regnault's results are here accepted, also ; 
and Buel's tables, the only tables known to the Author in 
which this correction has been applied, are, with the consent 
of their author and his publishers, here given. The tables of 
Porter, published in his treatise on the Richards Steam-en- 
gine Indicator, may be used where separate tables in con- 
venient and compact form are desired. The differences to be 
noted between the latter, which are compiled, with careful re- 
vision, directly from Regnault, and those of Rankine are not 
great; but the engineer should use either the one or the other 
exclusively in any one piece of work. 

In the study of the methods and principles of designing 
steam-boilers, an attempt is made to collate the most essential, 
and to apply them to the proportioning of the best forms of 
boilers now familiar to the engineer. This part of the work 
is of great importance to the designing engineer, and it has 
been the endeavor to give this treatment of it a shape that 
will prove at once sufBcient for its purpose, and yet fairly con- 
cise and very definite. It includes chapters on the design of 
the chimney and other accessories, and on specifications and 
contracts — subjects rarely touched upon in earlier manuals. 
The chapters on the operation and care of boilers, and their 
management generally, is largely based upon a somewhat ex- 
tensive personal experience during earlier life, on the part of 
the Author, when he was engaged, first in the business of con- 
stuction, and later in actual practice, during the civil war, as a 
member of the corps of U. S. Naval Engineers, as well as 
during two decades of desultory practice as a consulting en- 
gineer since that time. It is hoped that it may prove well 
suited to meet the needs of the class of young men to whom it 
is addressed. 

In the chapter on trials of steam-boilers, the methods re- 
ported favorably to the American Society of Mechanical En- 
gineers are adopted as standard, and the report of the com- 
mittee is taken almost bodily into the text. As this report, 
in part, was prepared by the Author from his lecture-notes 



VI PREFA CE. 

largely, and in consultation with the several distinguished en- 
gineers associated with him on that committee, it may, very 
probably, be admitted that this wholesale quotation is fully 
justified. The report will be found published in full in the 
Transactions of that Society, together with the discussion 
brought out by its presentation. 

The chapter on explosions is already in print, with a few 
additions, as a treatise on the subject, published by Messrs. J. 
Wiley & Son. It was considered that such publication would 
very possibly prove of some service in preventing this proba- 
bly absolutely preventable class of disasters, and that it would 
secure a wider circulation, and do so much the more good, if 
printed as a separate monograph. 

The work, as a whole, is a larger treatise than could be used 
profitably in the average technical school ; but it is thought 
that it may find its place in the special schools of mechanical 
engineering, in those which are properly entitled to be called 
professional schools, giving a training which really fits the 
student who may succeed in passing through them for en- 
trance into the ranks of a profession which demands of its 
cadets a more complete preparation and a higher standing 
than any other, even among the distinctively so-called learned 
professions. The Author is fully conscious of the vast discrep- 
ancy between his aim and his accomphshment ; but he hopes 
that the book may be of some service, nevertheless, to many 
engineers, old and young. 

Sibley College, Cornell University, 
January, 1888. 



CONTENTS, 



CHAPTER I. 

HISTORY OF THE STEAM-BOILER; STRUCTURE; DESIGN. 

SEC. PAGB 

1. Office of the Steam Boiler, . . i 

2. Development of Standard Forms, 2 

3. The older Types of Boiler, 4 

4. Special purposes and modern Types, ....... 7 

5. Method and Limit of Improvement 10 

6. Principles involved in designing, , ...... 11 

7. Production, transfer, and storage of Heat, .,.,.. 12 

8. Utilization of Heat, 15 

9. Safety in operation, iS 

10. Appurtenances of Steam Boilers, 18 

11. Classification of Boilers, 19 

12. Modern Standard Forms, , .20 

13. Mixed Types, ........... 20 

14. Mixed Application, .......... 20 

15. Common * Shell " Stationary Boilers, ...... 21 

16. The Locomotive Boiler. ......... 26 

17. Marine Boilers; older Forms, ........ 29 

18. Marine Water-tube Boilers, ........ 30 

19. The Scotch Boiler, .......... 32 

20. Sectional Boilers, .......... 35 

21. Marine sectional Boilers, ......... 38 

22. Periods of Introduction, ......... 39 

23. Special Forms of Boiler. ......... 42 

24. Problems in Design and Construction, 45 

25. Problems in the Use of Boilers, 43 

26. General Methods of Solution, 43 

CHAPTER II. 

MATERIALS OF STEAM-BOILERS; STRENGTH AND OTHER 
CHARACTERISTICS. 

27. Quality of Materials required, , r 45 

28. Principles relating to Strength, ........ 45 

29. Tenacity, Elasticity. Ductility, Resilience, 56 



Vlll 



CONTENTS. 



SEC. PACK 

30. Characteristics of Iron, physical and chemical, 57 

31. " " " Steel 63 

32. Effect of Variation of Form, ........ 64 

33. " " Method of Treatment, . 70 

34. " " Time and Margin of Stress, ....... 74 

35. Method of detecting Overstrain, . . . . , . . .81 

36. Effect of Temperature, 83 

37. Crystallization and Granulation, . . . . . . . .90 

38. Iron and Steel compared, . . .92 

39. Grades and Qualities of Iron Boiler-plate, ...... 94 

40. Manufacture of Iron and Steel plate, 96 

41. Methods of Test of Iron and Steel, 98 

42. Results of Tests, 104 

43. Specifications of Quality, 108 

44. Choice for Various Parts, 112 

45. Methods of Working, ...... .... 113 

46. Special Precautions in using Steel, ' . . . . . . . 113 

47. Rivets and Rivet Iron and Steel, . . , . . . .114 

48. Sizes, Forms, and Strength of Rivets, 115 

49. Strength of riveted Seams; Helical Seams, . . . . . .117 

50. Punched and Drilled Plates, 123 

51. Steam-riveting and Hand-riveting, ....... 125 

52. Welded Seams, ........... 127 

53. " Struck-up" or Pressed Shapes, . . 127 

54. Cast and Malleableized Iron, Brass, and Copper, . . . .127 

55. Shells of Boilers, 129 

56. Flues, Flanged and Corrugated, 140 

57. Stayed Surfaces, Stays and Braces, 144 

58. Relative Strength of Shell and Sectional Boilers, .... 148 

59. Loss of Strength and Ductility of Metal, 149 

60. Deterioration of Boilers, . . . . , . , . .150 

61. Inspection and Test of Boilers, ........ 151 

CHAPTER III. 
THE FUELS AND THEIR COMBUSTION. 



62. 


Combustion defined ; 


63. 


Fuels; Coal defined. 


64. 


Anthracite Coals, 


65. 


Bituminous Coals, 


66. 


Lignites, 


67. 


Peat or Turf, 


68. 


Wood, 


69. 


Coke, 


70. 


Charcoal, 


71. 


Pulverized Fuel, 



Perfect Combustion, 



152 

153 
155 
156 
158 
159 
159 
160 
162 
164 



CONTENTS, IX 

SEC. PAGE 

72. Liquid Fuels, • • . . 165 

73. Gaseous Fuels, ^ . . . . 167 

74. Artificial Fuels, 168 

75. Heating Power of Fuels, i6g 

76. Temperature of the Fire, . 172 

77. Minimum Air required, ..,.,,,.. 178 

78. Temperature of Products of Combustion, 179 

79. Rate of Combustion, ......... 184 

80. Efficiency of Furnace, ....,.,,. 185 

81. Economy of Fuel, . ......... 187 

82. Weather Wastes, 191 

83. Composition of Fuels, ......... 192 

84. Heating Effects of Fuels, 194 

85. Composition of Ash, 200 

86. Commercial Value of Fuels, . . . . . . , . 201 

87. Furnace Management, ......... 204 

88. Adaptation of Boiler, Furnace, and Fuel, 206 



CHAPTER IV. 

heat; ITS NATURE, PRODUCTION, MEASUREMENT AND TRANSFER; 
EFFICIENCY OF HEATING SURFACE. 

89. Nature of Heat, . 207 

90. Methods of Production ; Combustion, 208 

91. Temperatures ; Quantities of Heat ; Specific Heat, .... 210 

92. Thermometry ; Calorimetry, 214 

93. Transfer of Heat 215 

94. Radiation of Heat, .......... 216 

95. Conduction, 217 

96. Convection, ........... 219 

97. Transfer of Heat in the Steam Boiler, ' 220 

98. Formulas for Efficiency of Heating Surfaces, and Area of Cooling 

Surfaces, ........... 221 

99. Effect of Incrustation and Deposits, . . . . . . 228 

CHAPTER V. 

HEAT AS ENERGY; THERMODYNAMICS. 

ICO. Heat as a form of Energy, ........ 229 

loi. Energetics ; Heat-energy and Molecular Velocity, .... 233 

102. Heat-energy as related to Temperature, . . . . . . 235 

103. Quantitative measure of Heat-energy, ...... 236 

104. Heat transformations, ......... 237 

105. Heat and Mechanical Energy, 237 

106. Thermodynamics defined, . 238 



X CONTENTS, 

SEC. PAGE 

107. First Law of Thermodynamics, . 239 

108. Second Law of Thermodynamics, ....... 240 

109. Molecular Constitution of Bodies, 241 

no. Solids, Liquids and Gases defined ; the perfect gas, .... 241 

111. Heat and Matter ; Specific Heats, 242 

112. Sensible and Latent Heats, ....,.., 243 

113. Latent Heat of Expansion, ........ 243, 

114. Latent Heats of Fusion and Vaporization, ...... 244 

115. Distribution of Heat-energy, . . . . . . . . 244 

116. Application of First Law ; Equations, . . . . . . 245 

117. Application of Second Law, 247 

118. Computation of Internal and External Forces and Work, . . . 248 



CHAPTER VL 

STEAM ; VAPORIZATION ; SUPERHEATING ; CONDENSATION ; PRESSURE 
AND TEMPERATURE. 

119. Steam Generation and Application, ....... 252 

120. Properties of Water; Water as a Solvent, 253 

121. Composition and Chemistry of Water, . ■ 254 

122. Sources and Purity of "fresh" Water, ...... 25s 

123. Sea Water ; Deposits and Remedies, 256 

124. Technical Uses of Water; Filtration, ...... 260 

125. Water-analysis, .... 261 

126. Purification of Water, ......... 262 

127. Physical Characteristics of Water, 263 

128. Changes of Physical State, 265 

129. The " Critical Point," ......... 265 

130. The " Spheroidal State;" Superheated Water, 268 

131. Vaporization; Superheating Steam, ...... 269 

132. Thermal and Thermodynamic Relations, 270 

133. Internal Pressures and Work; Total and Latent Heats, . . . 271 

134. Computation of Internal Work and Pressure, . . . . , 271 

135. Specific Volumes of Steam and Water, ...... 272 

136. Relations of Temperatures, Pressures and Volumes, .... 273 

137. Specific Heats of Water and Steam, ....... 275 

138. Computation of Latent and Total Heats, 276 

139. Factors of Evaporation, 278 

140. Regnault's Researches and Methods, 280 

141. Regnault's Tables, 281 

142. Stored Energy in Steam; Tables, 285 

143. Curves of Energy, 289 

144. Power of Steam ; of Boilers, 291 

145. Horse-power of Boilers, 292 



CONTENTS. XI 



CHAPTER VII. 
CONDITIONS CONTROLLING BOILER DESIGN. 

SEC. PAGE 

146. The Problem stated, 300 

147. Selection of Type and Location, 300 

148. Choice of Fuel; Method of Combustion, 302 

149. Conditions of Efficiency ; Pressure chosen, 303 

150. Principles of Design, .......... 304 

151. Controlling Ideas in Construction, ....... 307 

152. Factors of Safety; Efficiency and Cost, ...... 311 

153. Water-tubes and Fire-tubes, 312 

154. Shell and Sectional Boilers, . . 314 

155. Natural and Forced Draught 314 

156. Special conditions affecting Design, ....... 317 

157. Chimney Draught, .......... 317 

158. Size and Form of Chimney, ........ 322 

159. Furnace and Grate, .......... 329 

160. Relative areas of Chimney, Flues and Grate, . . . . . 334 

161. Common Proportions and Work of Boiler, ..... 335 

162. Usual rates of Evaporation, ........ 338 

163. Quality of Steam and Efficiency, 338 

164. Boiler Power; Number and Size, 340 

165. Standard Sizes of Tubes; Spacing, 341 

166. Details of the Problem, . . 345 

CHAPTER VIII. 
DESIGNING STEAM BOILERS. 

167. General Considerations, 346 

168. Parts defined ; Common Matters of Detail, 346 

169. Designing the Plain Cylinder Boiler, 350 

170. Stationary Flue Boilers, ......... 354 

171. Cylinder Tubular Boilers, ......... 358 

172. Marine Flue Boilers, 361 

173. Marine Tubular Boilers, 362 

174. Sectional and Water-tube Boilers, ....... 364 

175. Upright and Portable Boilers, 369 

176. Locomotive Boilers, 37 1 

CHAPTER IX. 
ACCESSORIES ; SETTING ; DESIGN OF CHIMNEYS. 

177. Setting Steam Boilers; Suspension, ....... 376 

178. Covering, 380 

179. Form and Location of Bridge-wall, 381 



Xll 



CONTENTS. 



SEC. PAUh. 

180. Disposition of Flues, 381 

181. Location and Form of Dampers, ....... 381 

1S2. Steam and Water pipes, ......... 383 

183. Safety Valves, 385 

184. Feed Apparatus ; Heaters, 392 

185. Steam Gauges, Fusible Plugs, and minor accessories, . . . 393 

CHAPTER X. 
CONSTRUCTION OF BOILERS. 

186. Methods and Processes; Drawings, ....... 400 

187. Apparatus and Machinery, . . , 401 

188. Shearing; Planing; Fitting, 402 

189. Flanging and Pressing; Drilling and Punching, .... 402 

190. Forming bent parts, .......... 403 

191. Riveting and Riveting Machines; Welding, ..... 404 

192. Setting Tubes and Flues; Staying, ....... 413 

193. Chipping and Calking, ......... 417 

194. Assembling, 420 

195. Inspection 420 

196. Testing Steam Boilers, ......... 422 

197. Sectional Boilers, .......... 423 

198. Transportation and Delivery, . 424 

CHAPTER XL 
SPECIFICATION ; CONTRACTS ; INSPECTION. 

199. Purpose of Specification and Contract 425 

200. The Contract, ........... 426 

201. Form of Specifications, generally, 427 

202. Specification for Steam Boilers, 427 

203. Sample Specifications, 427 

204. Specification of Quality and Tests of Metal, 436 

205. Duties of the Inspector, 438 

CHAPTER XII. 
OPERATION AND CARE OF BOILERS. 



206. General Management, 

207. Starting Fires and getting up Steam, 

208. Managing Fires, .... 

209. Use of various kinds of Fuel, 

210. Liquid and Gaseous Fuels, . 

211. Solid Fuels, ... 



440 
441 
442 
444 
444 
44s 



I 




CONTENTS. Xlll 

PAGE 

Operation of the Boiler, , . , . 445 

213. Forced Draught, ........... 448 

214. Closed and Open Fire-rooms, 448 

215. Control of Steam Pressures, 449 

216. Regulation of Water-supply, ........ 449 

217. Emergencies, ........... 450 

218. Low Water, ........... 450 

219. Priming; Sudden Stopping, . . . . . . . .451 

220. Fractured Seams; Leaky tubes, ........ 453 

221. Deranged Safety Valves; Excessive Pressure 454 

222. General Care of Boilers, . . . . . . . . . 454 

223. Chemistry of Corrosion, . . . . . - . . . 454 

224. Method of Corrosion, 455 

225. Durability of Iron and Steel, ........ 457 

226. Preservation of Iron, .......... 458 

227. Paints and Preservatives; Coverings, ...... 458 

228. Leakage; Contact with Setting, ........ 461 

229. Galvanic Action. . . . . . . . . , , 462 

230. Incrustation; Sediment, ......... 462 

231. Repairs, ............ 465 

232. Inspection and Test, 466 

233. General Instructions, 469 

CHAPTER Xin. 
EFFICIENCIES OF STEAM BOILERS. 

234. Efficiencies of the Steam Boiler, 472 

235. Measures of Efficiency, 473 

236. Efficiency of Combustion, ......... 473 

237. Efficiency of Transfer of Heat, .....,,. 473 

238. Net Efficiency, .....•.,..,, 473 

239. Finance of Efficiency, ....,.,., 474 

240. Commercial Efficiency, ......... 474 

241. Algebraic Theory of Efficiencies, . . . . , , . 476 

242. Theory of Commercial Efficiency, ....,,. 477 

243. Efficiency of a Given Plant, , . 481 

CHAPTER XIV. 
STEAM-BOILER TRIALS. 



244. Purposes of Boiler Trials, 

245. Test of Value of Fuel, 

246. Determination of Value of Boiler, 

247. Evaporative Power of Fuels, 

248. Analysis of Fuels, 



484 
485 
485 
485 
486 



XIV 



CONTENTS, 



SEC. PAGE 

249. Efficiency and Economy of Fuel, 487 

250. Relative Values of Boilers, 489 

251. Variation of Efficiency with Consumption of Fuel and Size of Grate, 489 

252. Relation of Area of Heating Surface to Economy, .... 490 

253. Combined Power and Efficiency, ....... 490 

254. Apparatus and Methods of Test, 490 

255. Standard Test-trials, ......... 492 

256. Instructions and Rules for Standard Method, . . . . . 493 

257. Precautions; Blanks and Record, . . . . . . . 502 

258. Results of Test-trials, 504 

259. Quality of Steam, 517 

260. Form of Barrel Calorimeter and use, 519 

261. Theory of Calorimeters, . 521 

262. Records ; Errors, 523 

263. The Coil Calorimeter, . . . . . . . , . 524 

264. The Continuous Calorimeter, . . . . . . . , 527 

265. Analysis of Gases ; Form of Apparatus, . . . , , .531 

266. Efficiency as indicated by Gas-analysis, 535 

267. Draught Gauges, • • 535 



CHAPTER XV. 

STEAM-BOILER EXPLOSIONS. 

268. Steam-boiler Explosions, . . . 538 

269. Energy stored in Boilers, ......... 541 

270. Energy of Steam alone, 548 

271. Explosions defined and described ; Fulminating Explosions ; Col- 

lapsed Flues ; Bursting, 549 

272. Causes of Explosion : Probable ; Possible, and unusual ; improba- 

ble and absurd, .......;.. 550 

273. Statistics of Explosions and Causes, 553 

274. Theories and Methods of Explosion, ...... 558 

275. Colburn's Theory of Explosions, 559 

276. Lawson's and other Experiments 561 

277. Energy stored in heated metal, 567 

278. Strength of heated metal, 568 

279. Low-water ; Causes and Consequences, ...... 568 

280. Sediment and Incrustation, 574 

281. Energy stored in superheated water; Experiments of Donny and 

Dufour ; De-aeration of water, 578 

282. The Spheroidal State; Leidenfrost's and Boutigny's Experiments, . 583 

283. Steady rise of Pressure, 589 

284. Relative Security of Boilers, 592 

285. Defects of Design, 593 

286. Defective Construction, ........ 596 

2S7. Developed Weakness ; Corrosion, . . • 601 



CONTENTS. XV 

SEC. PAGE 

288. General and Local Decay, 604 

289. Methods of Corrosion and Decay ; Grooving or Furrowing, , . 606 

290. Differences of Temperatures, 609 

291. Management of Boilers, ......... 612 

292. Emergencies ; Precautions, ........ 614 

293. Results of Explosions ; Causes; Examples, ..... 616 

294. Experimental Explosions and Investigations 633 

295. Conclusions, 642 



APPENDIX. 

Table I. — Properties of Steam, .... ... 646 

" \a. — Regnault's Table, ..,...,.. 653 

" II. — Energy in Water and Steam, . 656 

Index, ...,«...<.... 659 



r 



THE STEAM-BOILER 



CHAPTER L 

HISTORY OF THE STEAM-BOILER — ITS STRUCTURE. 

I. The Office of a Steam-boiler is to transfer the heat- 
energy produced by the combustion of fuel to the mass of en- 
closed water, and, by the conversion of the latter into steam, 
to store that energy in available form for use, as in the steam^ 
engine. 

The source of this energy was, originally, that existing in 
the rays of the sun, and, by the action of chemical affinity as 
exhibited in the growth of vegetation, it has been transformed 
from its kinetic form, in heat and light rays, to the potential 
form, as now found in the recent or fossil fuels of forest and 
coal-bed. 

The process of absorption and storage of heat-energy in 
vegetable matter is reversed, in the furnace, in the combustion 
of the fuel ; and the combination of the carbon and hydrogen, 
constituting the familiar hydrocarbons, with the oxygen of the 
air entering the " firebox," retransforms their stored, poten- 
tial, energy into the available, kinetic, form of heat-motion, and 
it is then applied to the elevation of the temperature of the 
gaseous products of combustion and of the nitrogen passing 
through the boiler. By conduction and convection, and by 
radiation, in part, this heat is next transferred to the water in 
the boiler, raising its temperature, evaporating it, and " making 
steam" at a temperature fixed by the pressure under which the 
operation is carried on. By the formation of steam, a part of 
the heat is converted once more into the potential form by that 
method of performance of " internal work" in the separation of 
molecule from molecule, against the resistances due to cohesive 
forces, which measures the "latent heats" of evaporation and of 



2 THE STEAM-BOILER. 

expansion ; while the remainder is the sensible heat of the 
steam. Thus the fluid stored in the steam-boiler is a reservoir 
of energy which is drawn upon by the steam-engine when the 
latter is set in operation to transform that heat-energy into me- 
chanical energy ; and the steam sent from the boiler to the en- 
gine conveys to the latter this energy in the two forms of 
sensible and of latent heat, or of actual and potential energy. 

The steam-boiler should be capable of thus producing, stor- 
ing, and delivering heat-energy, in maximum quantity, and 
with maximum economy and safety. In other words, the 
steam-boiler should produce steam in the largest practicable 
quantity, with the least possible expenditure of fuel and of 
money, and with perfect safety. 

2. The Development of the Standard Forms of Steam- 
boiler has been a process of trial and error, in some sense one 
of evolution of numerous types, and of the survival of the fit- 
test, extending over many years. In the earlier days of the 

steam-engine the shapes assum- 
ed were invariably simple, and 
comparatively easy of construc- 
tion. Thus the boiler shown 
by Hero (Fig. i), in his " Pneu- 
matica," two thousand years ago, 
was spherical ; as were those of 
many later engines, all being evi- 
dently expected to be capable 
of sustaining considerable pres- 
sures.* 

Thus, in 1601, Giovanni Bat- 
tista della Porta, in his work 
** Spiritali," described an appara- 
tus by which the pressure of 
steam might be made to raise a 
column of water, and the method 

Fig. I. — The Grecian Idea of the ^ 

Steam-engine. of opcratiou mcludcd the appli- 

cation of the condensation of steam to the production of a 




* History of the Steam-engine. R. H. Thurston. 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 3 

vacuum into which the water would flow. He used a separate 
boiler. Fig. 2 is copied from an illustration in a later edition 
of his work.* 





Fig. 2. — Porta's Apparatus, a.d. 1601. Fig. 3. — De Caus's Apparatus, a.d. 1615. 

Again, in 161 5, Salmon de Caus, who had been an engineer 
and architect under Louis XIII. of France, and later in the 
employ of the British Prince of Wales, published a work at 
Frankfort, entitled " Les Raisons des Forces Mouvantes avec 
diverses machines tant utile que plaisantes," in which he illus- 
trated his proposition, " Water will, by the aid of fire, mount 
higher than its level," by describing a machine designed to 
raise water by the expanding power of steam. (See Fig. 3.) 
This consisted of a metal vessel partly filled with water, and 
in which a pipe was fitted leading nearly to the bottom and 
open at the top. Fire being applied, the steam, formed by its 



I Tre Libri Spiritali. Napoli, 1606. 



THE STEAM-BOILER. 




Fig. 4.— Worces- 

er's Engine, a.d. 

1650. 



elastic force, drove the water out through the vertical pipe^ 
raising it to a height depending upon either the wish of the 
builder or the strength of the vessel. 

In Worcester's apparatus, also (Fig. 4), we have a hardly 
less simple form of boiler, the operation of which is such as to 
render it subject to high pressure. 

Steam is generated in the boiler D, and 
thence is led into the vessel A, already nearly 
filled with water. It drives the water in a jet 
out through a pipe, F or F' . The vessel A is 
then shut ojff from the boiler and again filled " by 
suction" after the steam has condensed through 
the pipe G, and the operation is repeated, the 
vessel B being used alternately with A. 

The separate boiler, as here used, constitutes 
a very important improvement upon the pre- 
ceding forms of apparatus, although the idea 
was original with Porta. 
Denys Papin, contemporary with the Marquis of Worcester, 
and a distinguished man of science of that time, invented the 
common lever safety-valve, and applied it to his '' digester," as 
his closed vessel for cooking under pressure was called ; he 
used it later (1690) on the steam-boil- 
ers connected with his own steam- 
engine. It has been continuously in 
use ever since. 

3. Forms familiar in the Last 
Century approximate modern 
types. Thomas Savery, A.D. 1699, 
used ellipsoidal forms in his then 
"newly invented fire-engine," of 
which Fig. 5 is a good representa- 
tion, as first given by the inventor 
himself, in the " Miner's Friend." 

Z Z is the boiler, in which steam 
is raised, and through the pipes O O ^'^- s-— Savery's Engine, a.d. 1699. 
it is alternately let into the vessels P P. 

Suppose it to pass into the left-hand vessel first. The 




HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 5 

valve M being closed and r being opened, the water contained 
in P is driven out and up the pipe 5 to the desired height, 
where it is discharged. 

' The valve r is then closed, and also the valve in the pipe O, 
The valve M is next opened, and condensing water is turned 
upon the exterior of P by the cock K, leading water from the 
cistern X. As the steam contained in P is condensed, forming 
a vacuum, a fresh charge of water is driven by atmospheric 
pressure up the pipe T. 

Meantime, steam from the boiler has been let into the right- 
hand vessel jP, the cock W having been first closed and R 
opened. The charge of water is driven out through the lower 
pipe and the cock R^ and up the pipe 5 as before, while the 
other vessel is refilling preparatory to acting in its turn. 

The two vessels thus are alternately charged and discharged 
as long as is necessary. Savery's method of supplying his 
boiler with water was at once simple and ingenious. 

The small boiler D is filled with water from any convenient 
source, as from the stand-pipe S. A fire is then built under it, 
and, when the pressure of steam in D becomes greater than in 
the main boiler Z, a communication is opened between their 
lower ends and the water passes under pressure from the 
smaller to the larger boiler, which is thus " fed " without inter- 
rupting the work. G and N ^r^ gauge-cocks by which the height 
■of water in the boilers is determined, and these attachments 
were first adopted by Savery. 

It will be noticed that Savery, like the Marquis of Worces- 
ter, and like Porta, used a boiler separate from the water-reser- 
voir. 

A working model was submitted to the Royal Society of 
London in 1699,^ and successful experiments were made 
with it. 

Newcomen's engine, of 1705 and later, superseded the 
Savery apparatus in consequence of his adaptation of his ma- 
chine to the use of low (atmospheric) pressure steam, quite as 
much as because of its greater economy. By introducing the 

* Transactions of the Royal Society, 1699. 



6 



THE STEAM-BOILER. 



beam-engine, and pumps separate from the steam-vessel, he 

was able to avoid all danger of explo- 
sion, using his steam at a pressure but 
little exceeding that of the atmos- 
phere, and applying it simply to the 
displacement of the air, preliminary to 
the production of a vacuum. It thus 
became safe to use any convenient 
form of steam-vessel, and in Fig. 6 it 
is seen that he at once departed most 
signally from those shapes which had 
necessarily been earlier used, and took 

Fig. 6.— newcomen's Engine and advantage of this freedom in design to 

Boiler, a.d. 1705. ° r 1 -i r ^ 

secure a type of boiler of greater pro- 
portional area of heating-surface, as shown at d, and conse- 
quently of greater economy in use of fuel. It is seen that he 
used gauge-cocks, c c, and safety-valves, N. 

James Watt's first boiler illustrates another step in this 
latter direction. 

In this. A, Fig. 7, the "wagon-boiler," as he called it, the 





Fig. 7.— Watt's First 
Model, 1765. 




Fig. 8.— Oliver Evans's Engine, 1800. 



vessel is so shaped as to permit flues to be formed on either 
side, as well as below, for the circulation of the products of 
combustion backward and forward from end to end of the 
boiler. 

A still further advance is illustrated in the now well-known 
*' Cornish Boiler," Fig. 8, as used by Oliver Evans in the United 
States, and by British engineers of his time (1800), of which 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. / 

the "shell" is cylindrical, and through which a single flue, of 
about one half the diameter of the boiler, passes from one end 
to the other. The gases traverse this flue and also partly en- 
velop the exterior of the shell, thus coming in contact with a 
comparatively large extent of heating-surface. This form was 
followed by the ''two-flued" Evans or Lancashire boiler, which 
was a cylinder containing tw^o flues, each about one third its 
diameter, and by others in which the number of flues was in- 
creased with continually decreasing diameter, and with con- 
stant gain in total heating-surface until the modern types of 
tubular boiler were developed. 

4. Special Purposes produce the Modern Types of 
boilers. Thus a desire to secure maximum efficiency produced 
the tubular boilers, and the desire to secure safety the so-called 
"sectional boilers." As early as 1793, Barlow invented, and 





Fig. 9. 



•Water-tube Boiler of Fulton 
Barlow, 1793. 



Fig. 10. — Stevens's " Sectional' 
Boiler, 1804. 



with Fulton used, the " water-tube"boiler (Fig. 9), in which the 
water circulates through the tubes, instead of around them, 
as in " fire-tube" boilers. This w^as the pioneer of a great variety 
of boilers of this class. 

John Stevens, a distinguished statesman as well as engineer, 
of the early part of the nineteenth century, devised another ex- 
ample of this class, showm in Fig. 10, as early as the year 1804. 

The inventor says in his specifications : " The principle of 
this invention consists of forming a boiler by means of a system 
or combination of small vessels, instead of using, as is the com- 
mon mode, one large one ; the relative strength of the materials 
of which these vessels are composed increasing in proportion to 
the diminution of capacity." The steamboat boiler of 1804 was 



8 



THE STEAM-BOILER. 



built to bear a working pressure of over fifty pounds to the 
square inch, at a time when the usual pressures were from four 
to seven pounds. It consists of two sets of tubes, closed at one 
end by solid plugs, and at their opposite extremities screwed 
into a stayed water and steam reservoir, which was strengthened 
by hoops. The whole of the lower portion was inclosed in a 
jacket of iron lined with non-conducting material. The fire 




Fig. II. — Gurney's Steam carriage, 1833. 

was built at one end, in a furnace inclosed in this jacket. The 
furnace-gases passed among the tubes, down under the body of 
the boiler, up among the opposite set of tubes, and thence to 
the smoke-pipe. In another form, as applied to a locomotive 
in 1825, the tubes were set vertically in a double circle s.ur- 




FiG. 12.— Stephenson's Locomotive, 1815. 

rounding the fire. These boilers are carefully preserved among 
the collections of the Stevens Institute of Technology. 

Still another modification of this type is illustrated in the 
boiler used by Gurney in steam-carriages (Fig. ii) built about 
the years 1830-5, in which the steam-generator consisted of bent 
steam-pipe of small diameter so connected with steam and mud 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 



9 



drums as to make a very efficient as well as safe and powerful 
boiler for use where lightness, strength, and safety were essen- 
tial characteristics. 

•Similarly, the special demands of locomotive construction 
were not fully met by the single-flue boiler first used by George 
Stephenson (Fig. 12) and by his colleagues in 181 5, and up to 




Fig. 13. — Stockton and Darlington Engine No. i, 1825. 

the time of construction of the Stockton and Darlington Rail- 
way in 1825 (Fig. 13), an example of which is still preserved in 
the first engine built for that road. At the opening of the Liv- 
erpool and Manchester Railway (1829), Stephenson's Rocket 
was given the multitubular boiler, a form which had grown into 
shape in the hands of several inven- 
tors.* This boiler was three feet in 
diameter, six feet long, and had 
twenty-five three-inch tubes, extend- 
ing from end to end of the boiler. 
The steam-blast was carefully adjusted 
by experiment, to give the best effect. 
Steam-pressure was carried at fifty 
pounds per square inch. 

The average speed of the Rocket 
on its trial was fifteen miles per hour, ^'^- i4-The rocket, 1829. 
and its maximum was nearly double that — twenty-nine miles 
an hour; and afterward, running alone, it reached a speed of 
thirty-five miles. 

* Barlow and Fulton, 1795 ; Nathan Read, Salem, United States, 1796; 
Booth of England, and Seguin of France, about 1827 or 1828. 




lO THE STEAM-BOILER. 

The shares of the company immediately rose ten per cent 
in value. The combination of the non-condensing engine with 
a steam-blast and the multitubular boiler, designed by the clear 
head and constructed under the eye of an accomplished engi- 
neer and mechanic, made steam locomotion so evident and 
decided a success, that thenceforward its progress has been un- 
interrupted and wonderfully rapid.* 

The special requirements of stationary steam-engine con- 
struction and operation, and of steam navigation, have, from 
these primitive types and forms, developed in the course of 
years the several now common and standard boilers which will 
be later described. 

5. The Method and Extent of Improvement is now easily 
traced. Looking back over the history of the steam-engine, we 
may rapidly note the prominent points of improvement and 
the most striking changes of form ; and we may thus obtain, 
some idea of the general direction in which we are to look for 
further advance. f 

Beginning with the machine of De Caus, at which point we 
may first take up an unbroken thread, it will be remembered 
that we there found a single vessel performing the functions of 
all the parts of a modern pumping-engine ; it was at once 
boiler, steam-cylinder, and condenser, as well as both a lifting 
and a forcing pump. The Marquis of Worcester, and, stilL 
earlier, Da Porta, divided the engine into two parts ; using one 
part as a steam-boiler, and the other as a separate water-vesseL 
Savery duplicated those parts of the earlier engine which acted 
the several parts of pump, steam-cylinder, and condenser, and 
added the use of the jet of water to effect rapid condensation. 
Newcomen and Cawley next introduced the modern type of 
engine, and separated the pump from the steam-engine proper ; 
in their engine, as in Savery's, we notice the use of surface- 
condensation first, and, subsequently, that of a jet of water 
thrown into the midst of the steam to be condensed. Watt 
finally effected the crowning improvement of the single-cylinder 

* History of the Steam-engine. R. H. Thurston. N. Y.: D. Appleton & 
Co.. 1878. 
t Ibid. 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. II 

engine, and completed this movement of differentiation by 
separating the condenser from the steam-cylinder, thus perfect- 
ing the general structure of the engine. 

Here this movement ceased, the several important processes 
of the steam-engine now being conducted each in a separate 
vessel. The boiler furnished the steam ; the cylinder derived 
from it mechanical power ; the vapor was finally condensed in 
a separate vessel ; while the power, which had been obtained 
from it in the steam-cylinder, was transmitted through still 
other parts to the pumps, or wherever work was to be done. 

Watt and his contemporaries also commenced that move- 
ment toward higher pressures of steam, used with greater ex- 
pansion, which has been the most striking feature noticed in 
the progress made since his time. Newcomen used steam 
of barely more than atmospheric pressure, and raised 105,000 
pounds of water one foot high, with a pound of coal consumed. 
Smeaton raised the steam-pressure to eight pounds, and in- 
creased the duty to 120,000. Watt started with a duty of 
double that of Newcomen, and raised it 320,000 foot-pounds 
per pound of coal, with steam at ten pounds. To-day, Cornish 
engines of the same general plan as those of Watt, but worked 
with forty to sixty pounds pressure, expanding three to six 
times, bring up the duty to 600,000 foot-pounds ; while more 
modern compound engines have boilers carrying 150 pounds 
(ten atmospheres) above the normal air-pressure, and the duty 
has been since raised to above 1,200,000 foot-pounds per pound 
of fuel used. 

6. The Requisites of Good Design are readily prescribed 
and defined : they are very simple, and although attempts are 
almost daily made to obtain improved results by varying the 
design and arrangement of heating-surface, the best boilers of 
nearly all makers of acknowledged standing are practically 
equal in merit, although of diverse forms. 

In making boilers the effort of the engineer should evidently 
be— 

1st. To secure complete combustion of the fuel without 
permitting dilution of the products of combustion by excess of 
air. 



12 THE STEAM-BOILER. 

2d. To secure as high temperature of furnace as possible. 

3d. To so arrange heating-surfaces that, without checking 
draught, the available heat shall be most completely taken up 
and utilized. 

4th. To make the form of boiler such that it shall be con- 
structed without mechanical difficulty or excessive expense. 

5 th. To give it such form that it shall be durable, under 
the action of the hot gases and of the corroding elements of 
the atmosphere. 

6th. To make every part accessible for cleaning and repairs. 

7th. To make every part as nearly as possible uniform in 
strength, and in liability to loss of strength by wear and tear, 
so that the boiler when old shall not be rendered useless by 
local defects. 

8th. To adopt a reasonably high " factor of safety" in pro- 
portioning. 

9th. To provide efficient safety-valves, steam-gauges, and 
other appurtenances. 

loth. To secure intelligent and very careful management. 

7. Effective Development, Transfer, and Storage of 
Heat, in the best possible combination, is evidently what -is 
demanded in the operation of the steam-boiler. 

In securing complete combustion an ample supply of air 
and its thorough intermixture with the combustible elements 
of the fuel are essential ; for the second, high temperature of 
furnace, it is necessary that the air-supply shall not be in excess 
of that absolutely needed to %\-v^ complete combustion. The 
efficiency of a furnace burning fuel completely is measured by 

^~ T-t' 

in which E represents the ratio of heat utilized to the whole 
calorific value of the fuel ; T is the furnace-temperature ; T 
the temperature of the chimney, and t that of the external air. 
Hence the higher the furnace-temperature and the lower that 
of the chimney, the greater the proportion of available heat. 
It is further evident that, however perfect the combustion, 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 1 3 

no heat can be utilized if either the temperature of chimney ap- 
proximates to that of the furnace, or if the temperature of the 
furnace is reduced by dilution approximately to that of the 
chimney. Concentration of heat in the furnace is secured, in 
some cases, by special expedients, as by heating the entering 
air, or, as in the Siemens gas-furnace, heating both the combus- 
tible gases and the supporter of combustion. Detached fire- 
brick furnaces have an advantage over the "fireboxes" .of 
steam-boilers in their higher temperature ; surrounding the fire 
with non-conducting and highly heated surfaces is an effective 
method of securing more perfect combustion and high furnace- 
temperature. 

In arranging heating-surface the effort should be to impede 
the draught as little as possible, and so to place them that the 
circulation of water within the boiler should be free and rapid 
at every part reached by the hot gases. 

The directions of circulation of water on the one side and 
of gas on the other side the sheet should, whenever possible, be 
opposite. The cold water should enter where the cooled gases 
leave, and the steam should be taken off farthest from that 
point. The temperature of chimney-gases has thus been re- 
duced by actual experiment to less than 300° Fahr., and an 
ef^ciency equal to 0.75 to 0.80 the theoretical is attainable. 

The extent of heating-surface simply, in all of the best 
forms of boiler, determines the efficiency, and the disposition 
of that surface in such boilers seldom affects it to any great 
extent. The area of heating-surface may also be varied within 
wide limits without greatly modifying efficiency. A ratio of 
25 to I in flue and 30 to i in tubular boilers represents the 
relative area of heating and grate surfaces in the practice of the 
best-known builders. This proportion may be often settled by 
exact calculation. 

The material of the boiler, as will be shown later, should be 
tough and ductile iron, or, better, a soft steel containing only suffi- 
cient carbon to insure melting in the crucible or on the hearth 
of the melting-furnace, and so little that no danger may exist 
of hardening and cracking under the action of sudden and great 
changes of temperature. 



14 THE STEAM-BOILER. 

Where iron is used it is necessary to select a somewhat 
hard but homogeneous and tough quality for the firebox 
sheets or any part exposed to flames. 

The factor of safety is very often too low. The boiler 
should be built strong enough to bear a pressure at least six 
times the proposed working-pressure ; as the boiler grows weak 
with age, it should be occasionally tested to a pressure far 
above the working-pressure, which latter should be reduced 
gradually to keep within the bounds of safety. The factor of 
safety is seldom more than four in new boilers ; and even this 
is reduced practically by the operation of the inspection laws. 

Effective development of heat is secured primarily by the 
selection of good fuel, by which is usually meant fuel which 
consists, to the greatest possible extent, of available combusti- 
ble material ; but for the purposes of the engineer who designs 
the boiler, or of the owner for whom it is to be constructed, the 
real criterion of quality is the quantity of heat which the com- 
bustible, as burned in the furnace, will yield for any given sum 
of money expended in obtaining that heat. The cost of a fuel 
to the consumer consists, not simply of money paid for it to 
the dealer who supplies it, but also of cost of transportation 
and of placing in the grate, of removal of ash, of incidental ex- 
penses inseparable from its use, such as injury to boilers and 
other property, increased risks, and other such expenses, many 
if not most of which are very difficult of determination with 
any satisfactory decree of accuracy. Other things being equal, 
that fuel which gives the greatest quantity of available heat for 
the total money expenditure is that which permits most effec- 
tive development in the sense here taken. Effective heat-de- 
velopment from any selected fuel is secured, as already stated, 
by its complete combustion in such manner as to give the 
highest possible temperature. 

Effective transfer of heat is secured by such a form of 
steam-generator, and such extent and disposition of '* heating- 
surfaces," as will most completely utilize the heat developed in 
the furnace and flues by causing it to flow, with the least pos- 
sible loss, into the water and steam contained within the boiler ; 
and this is effected by proper arrangement of surfaces absorb- 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 1 5 

ing heat from the gases and yielding it to the liquid as already 
generally described. 

Effective storage of heat can be secured by providing large 
volumes of water and of steam, v/ithin which the heat transferred 
from the furnace and flues can be stored, and by carefully pro- 
tecting the whole heated system from waste by conduction or 
radiation to adjacent bodies. Where the demand is steady, and 
the supply from the fuel fairly steady also, the amount stored 
need not be great, as the use of the reservoir is simply that of 
a regulator between furnace and engine or other apparatus re- 
ceiving it ; but where either supply or demand is variable, con- 
siderable storage capacity may be needed. 

8. Efficient Utilization of Heat is as essential to the satis- 
factory working of any system of generation and application of 
heat as is efificient production, transfer, and storage. The mode 
of attaining maximum efficiency depends upon the nature of 
the demand and the method of expenditure ; and the considera- 
tion of this subject in detail would be here out of place. In 
general it may be said that where the heat and steam are re- 
quired for the impulsion of an engine, the higher the safe pres- 
sure and the practically attainable temperature at which the 
supply is effected, the more efficient the utilization of the heat. 
These limits of temperature and pressure are the higher as the 
actual working conditions are made the more closely to approxi- 
mate to the ideal conditions prescribed by pure science. 

Where heating simply, without, transformation into work, is 
intended, the principal and only very important requisite, 
usually, is to provide such thorough protection for the system 
of transfer and use, that no wastes of importance can take place 
by radiation or conduction. The character of the steam made, 
as to humidity, is in this case comparatively unimportant ; but 
in the preceding case it will be found essential that it should be 
always dry, and it is often much the better for being super- 
heated considerably above the boihng-point due to its pressure. 

The actual standing of the best steam-engine of the present 
time, as an efficient heat-engine, is really very high. The 
sources of loss are principally quite apart from the principles of 
design and construction, and even from the operation of the 



1 6 THE STEAM-BOILER, 

machine ; and it may be readily shown that, to secure any really 
important advance toward theoretical efficiency, a radical change 
of our methods must be adopted, and probably that we must 
throw aside the heat-engine in all its forms, and substitute for 
it some other apparatus by which we may utilize some mode of 
motion and of natural energy other than heat. 

The very best classes of modern steam-engines very seldom 
consume less than two pounds (0.9 kilog.) of coal per horse- 
power per hour, and it is a good engine that works regularly 
on three pounds (1.37 kilog.). 

The first-class steam-engine, therefore, yields less than 10 
per cent of the work stored up in good fuel, and the average 
engine probably utilizes less than 5 per cent. A part of this 
loss is unavoidable, being due to natural conditions beyond the 
control of human power, while another portion is, to a consid- 
erable extent, controllable by the engineer or by the engine- 
driver. Scientific research has shown that the proportion of 
heat stored up in any fluid, which may be utilized by perfect 
mechanism, must be represented by a fraction, the numerator 
of which is the range of temperature of the fluid while doing 
useful work, and the denominator of which is the temperature 
of the fluid when entering the machine, measured from the 
" absolute zero." 

Thus, steam, at a temperature of 320° Fahr., being taken 
into a perfect steam-engine, and doing work there until it 
is thrown into the condenser at 100° Fahr., would yield 

; — ^— = 0.28 +, or rather more than one fourth of the 

320-1-461 

work which it should have received from each pound of fuel. 
The proportion of work that a non-condensing but other- 
wise perfect engine, using steam of 75 pounds (5 atmos.) pres- 

^20 212 

sure, could utilize would be ^^ -— 1= 0.14 — 4-; and, while 

320 + 461 

the perfect condensing engine would consume two thirds of a 
pound (0.3 kilog.) of good coal per hour, the perfect non-con- 
densing engine would use \\ pounds (0.6 kilog.) per hour for 
each horse-power developed, the steam being taken into the 
engine and exhausted at the temperatures assumed above. 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 1/ 

Also, were it possible to work steam down to the absolute zero 
of temperature, the perfect engine would require but 0.19 
pound (0.09 kilog.) of similar fuel. 

It may therefore be stated, with a close approximation to 
exactness, that of all the heat derived from the fuel about 
seven tenths is lost through the existence of natural conditions 
over which man can probably never expect to obtain control, 
two tenths are lost through imperfections in our apparatus, and 
only one tenth is utilized in even good engines. Boiler and 
engine are intended to be included when writing of the steam- 
engine above. In this combination a waste of probably two 
tenths at least of the heat derived from the fuel takes place in 
the boiler and steam-pipes, on the average, in the best of prac- 
tice, and we are therefore only able to anticipate a possible 
saving of 0.2 X 0.75 = 0.15, about one sixth of the fuel now 
expended in our best class of engines, by improvements in the 
machine itself. The best steam-engine, apart from its boiler, 
therefore, ha^ 0.85, about five sixths, of the efficiency of a perfect 
engine, and the remaining sixth is lost through waste of heat 
by radiation and conduction externally, by condensation within 
the cylinder, and by friction and other useless work done within 
itself. Tt is to improvement in these points that inventors must 
turn their attention if they would improve upon the best modern 
practice by changes in construction. 

To attain further economy, after having perfected the 
machine in these particulars, they must contrive to use a fluid 
which they may work through a wider range of temperature, as 
has been attempted in air-engines by raising the upper limit of 
temperature, and in binary vapor engines by reaching toward a 
lower limit, or by working a fluid from a higher temperature 
than is now done down to the lowest possible temperature. 
The upper limit is fixed by the heat-resisting power of our 
materials of construction, and the lower by the mean tempera- 
ture of objects on the surface of earth, being much lower at 
some seasons than at others. In the boiler the endeavor must 
be made to take up all the heat of combustion, sending the 
gases into the chimney at as low a temperature as possible, and 
securing in the furnace perfect combustion without excess of 



1 8 THE STEAM-BOILER. 

air-supply. The best engines still lack 1 5 per cent Df perfec- 
tion, and the best boilers, as an average, over 30 per cent. 

9. Safety in Operation is one of the most essential require- 
ments which the designer, constructor, and user of steam-boilers 
must be prepared to fulfil. As will be seen later, the quantity 
of stored heat-energy in the steam-boiler is usually enormous, 
and this energy is stored under such conditions that, if set free 
by the rupture of the containing vessel, wide-spread disaster 
may ensue. This stored energy is at all times ready to instantly 
assume the kinetic form when permitted, and by doing mechani- 
cal work on all adjacent objects, to produce most extraordinary 
effects ; it is stored energy of the most perfectly elastic kind, as 
well as of high tension. The most absolutely reliable means 
known to the engineer must be adopted for the safe and per- 
manent control of such magazines of latent power. 

Those methods of securing safety which have been found 
most satisfactory have been — 

(i) The division of the confined energy among compara- 
tively small masses of steam and water contained in correspond- 
ingly small communicating chambers, so constructed that the 
rupture of one will be unlikely to produce fracture of any otHer. 

(2) The adoption of the very best material and of the best 
possible construction, and so proportioning all parts exposed to 
stress and strain that they may withstand pressures several 
times as great as the maximum intended to be carried. 

(3) Careful and intelligent operation and preservation. 

10. The Appurtenances or Accessories of Steam- 
boilers are those attached parts and apparatus which, while 
not, strictly speaking, actually essential elements of the struc- 
ture specially designated as the boiler, are nevertheless essen- 
tial to its safe and economical operation : such as, for example, 
safety and other valves, gauge-cocks, feed-pumps, dampers, 
grates, and " settings." 

Safety-valves are automatically self-operating apparatus 
which open and permit the steam to issue from the boiler 
whenever the pressure reaches a limit at which they are ar- 
ranged to act. Steam-valves are the valves, usually operated 
by screws, which, when open, permit the steam to leave the 
boiler and pass away through the steam-pipes. Stop-valves are a 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 1 9 

variety of valve which may be used to stop the passage of steam 
from the boiler: they may be "screw stop-valves," or simple 
valves moved directly by hand. Check-valves, commonly in- 
troduced at the junction of the feed-water supply-pipe with 
the boiler, are so arranged as to open automatically when the 
stream enters, but to close against a return current : they are 
sometimes pinned to their seats, when desirable, by a screw, in 
which case they are called '' screw-checks." Gauge-cocks are 
set at, and above or below, the intended working water-level 
of the boiler, and, when opened, by discharging steam or water, 
indicate the actual position of the water-line. Glass water- 
gauges are glass tubes set in such manner that the water 
stands in a vertical tube at the same height as the water in the 
boiler, the top of the glass communicating with the steam- 
space, and the lower end with the water-space of the boiler. 

II. The Classification of Steam-boilers may be based 
upon either a comparison of their forms or of their purpose. 
Under the former we have the plain cylindrical, the flue, the 
tubular, or the sectional boiler; under the latter, stationary, 
locomotive, or marine boilers. For the purposes of this work, 
the following may be taken as a satisfactory scheme : 



Stationary . 



Locomotive . 



Marine . . 



Plain cylindrical boilers. 
Cornish or single-flue. 
Lancashire or two-flue. 
Multiflueand return-flue boilersc 
Cylindrical fire-tube boilers. 
Firebox boilers. 
Sectional boilers. 
Peculiar forms. 
Common type. 
Wooton boilers. 
Special devices. 

r Flue. 
Older types I Flue and tube. 

( Tubular. 
Scotch or drum boilers. 
Water-tube and sectional. 
Miscellaneous forms. 



20 THE STEAM-BOILER. 

12. The Modern Standard Types of Boiler are becom- 
ing rapidly settled in a few well-defined forms which have 
been found to be most satisfactory, all things considered, each 
in its own special province. These are specified in the list just 
presented. But many boilers have become so thoroughly well 
adapted to the special work to which they are customarily 
applied as to have almost or quite entirely displaced other 
forms, which in turn are as generally adopted for other uses. 
Thus, where the feed-water supplied to land boilers, in locali- 
ties where fuel is cheap, or water bad, and certain to produce 
serious incrustation, the plain cylindrical boiler is almost univer- 
sally employed ; where the fuel is costly and the feed-water 
pure, the tubular boiler is as universally adopted ; while inter- 
mediate conditions lead to the use of intermediate forms. The 
locomotive boiler is standard for its place and purpose, and 
no other form has ever yet competed with it in thorough 
adaptation to that peculiar case. The high pressures carried 
and the necessity of great economy at sea have made the so- 
called " Scotch" or " drum" boiler standard in trans-oceanic 
steam navigation. Where small area of floor-space and ample 
" head-room" are found, the upright cylindrical tubular boiler 
is the standard form ; if the head-room is less and the floor- 
space larger, a modification of the locomotive type finds appli- 
cation for stationary purposes. 

13. Mixed Types of boiler are often constructed for special 
purposes or experimentally. In the shallow-water navigation 
of the United States of America, as on the Hudson River^ 
the flue and tube boiler is much used ; the locomotive type of 
boiler, with fewer and larger tubes than are adopted in locomo- 
tive practice, has often found use in stationary practice. New 
designs are continually coming forward which illustrate such 
forms of boiler. As a rule, however, they are not found pref- 
erable to the simpler and standard types. 

14. Mixed Applications are sometimes required, as where 
the same boiler supplies steam for power and for heating pur- 
poses. In this case the pressure carried on the boiler is fixed 
at the proposed maximum for the engine, and the lower pres- 
sures required for the other purpose are secured by the use 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 21 

of a " reducing" or " pressure-reducing" valve. The steam- 
heating systems of cities often illustrate this case, furnishing 
steam, as they do, for heating buildings, for cooking, and to 
steam-engines at all parts of the area covered by them. 

15. Common. Forms of "Shell" Boilers, as those boilers 
are called in which the structure consists of an external case 
enclosing steam and water, flues and tubes, are the following : 

(i) TJie Plain Cylindrical Boiler consists, as shown in section 
(Fig. 15), and in front elevation (Fig. 16), of a simple cylin- 




FiG. 15.— Section of Cylindrical Boiler. 



drical vessel, A, made of boiler-plate, fitted with heads at each 
end, B, B ; which heads are sometimes of sheet-iron and some- 
times of cast-iron. A steam-dome, C, on the upper side, 
usually serves as a collector and reservoir for the steam, as it 
rises from the water into the steam-space, and serves also as 
the point of attachment for the steam-pipe, D D, and safety- 
valve, E E, both of which thus take steam from the highest 
and driest part of the interior of the boiler. 

The fire is built in the detached furnace, F F, the products 
of combustion passing under the boiler to the rear, at G, where 



22 



THE STEAM-BOILER. 



a flue leads off to the chimney. The ^' setting" consists of 
side-walls and ends, H H, of brick, and a covering, / /, which 
is often merely a filling of ashes or other non-conductor, or an 
arch of brickwork carried over from the side-walls. ^' Binders," 
K K^ and rods, L L, tie the whole together, and resist any 
change of form due to variations of temperature. The grates, 




Fig. i6. — Front of Cylindrical Boiler and Setting. 



M M, are supported at the rear by the bridge-wall, N N, of 
which the upper part is usually built of fire-brick. The rear 
end of the boiler is often carried on rollers, to prevent danger of 
injury with the changes of form due to variations of tempera- 
ture such as are produced by the introduction of cold feed- 
water. 

(2) The Cylindrical Flue Boiler (Fig. 17) is a plain cylinder, 
like the preceding form, but with one or more flues passing 
through it from end to end. The setting is usually quite 
similar to that of the plain cylinder, except as necessarily 
modified to meet the requirements of the flue. The shell is 
generally shorter than that of the first-described boiler, the 
heating-surface considerably greater. 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 23 

(3) The Cylindrical Tubular Boiler is shown in one of the 
best forms in Fig. 180 It consists of a cyhndrical shell con- 



FiG. 17. — Cylindrical Flue Boiler. 



structed much as in Fig. 15, with a set of tubes carried from 
end to end, and set as closely as is practicable without inter- 
fering too seriously with the circulation of the water within it. 




Fig. 18. — Cylindrical Tubulak Ddiler. 



The peculiar feature of the illustration is the introduction of 
the very large single sheet which is seen to make the whole 
lower two thirds or more of the shell ; this construction pre- 



24 



THE STEAM-BOILER. 



venting the fire reaching seams and riveting, as occurs in the 
usual construction. 




Fig. 19. — Cylindrical Tubular Boiler and Setting. 



The setting of this kind of boiler is shown in Figs. 19 and 
20. The weight of the boiler is here taken by " lugs" on each 

side and by them transferred to the 
brickwork of the setting. In other 
cases the boiler is suspended from 
girders crossing the structure later- 
ally ; and the suspension-rods carry- 
ing the boiler are sometimes allowed 
vertical play, under the action of 
expansion and contraction of the 
whole system, by the introduction 
of springs of rubber or steel, thus 
permitting very uniform distribu- 
tion of the weight at all times. In 
many cases the gases, instead of 
being carried over the boiler to the 
chimney, as shown in Fig. 19, are 
taken directly to the chimney from the front of the boiler, as 




Fig. 20. — Section ok Tubulai 
and Setting. 



BOILEI 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 2$ 

in Fig. 1 6. It is not always thought safe to expose the top 
and steam spaces of the boiler to the heat of the escaping 
gases ; but the practice is not an uncommon one, even with 
reputable builders. The air-spaces in Fig. 20, at either side 
in the walls of the setting, give an additional protection from 
loss of heat, and a certain amount of elasticity of setting. This 
is the most common of all forms of steam-boiler. 




Fig. 21. — Firebox Tubular Boiler. 

(4) The Firebox Flue Boiler is so made in order that 
the whole may become "self-contained," and brickwork dis- 
pensed with. Adding the firebox to the tubular (Fig. 21), 
forms the locomotive type of 
boiler. In stationary boilers, 
however, the tubes are, as a 
rule, larger and less numerous 
than in the locomotive boiler. 
These boilers require no set- 
ting or connections other than 
the parts needed to connect 
them with the chimney-flue. 
This arrangement is seen in Fig. 22. The advantages of this 
type are the low cost of installation, the more complete ac- 




FlG. 



-Firebox Boiler Setting. 



26 



THE STEAM-BOILER. 



cessibility of the exterior for inspection and repair, the reduc- 
tion of floor-space occupied, and the portabiHty of the boiler. 





Fig. 23.— The Upright Boiler. 



Fig. 24. — Upright Tubular 
Boiler. 



(5) The Upright Boiler is usually a firebox tubular boiler, 
designed to stand vertically, as in Fig. 23, and to occupy m'ini- 




FiG. 25.— Battery ok Boilers. 
The above cut represents a pair of Cornish boilers set in brick-work, connected so as to be 
worked either together or separately, 

mum floor-space. Its construction at the upper end is often such 
as to permit the upper extremities of the tubes to be kept be- 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 2/ 







Fig. 26, 

WITH Field Tubes. 



low the water-line. In many cases, however, the tubes are car- 
ried directly through to the upper head, as is seen in Fig. 24. 
This figure also exhibits the method of attaching gauges and 
safety-valves. This boiler is much used where it is important 
to save floor-space, and where head-room can be obtained. It 
is the usual form in steam fire-engines. 

16. A '* Battery" of Boilers (Fig. 25) 
consists of two or more, placed side by side^ 
the total power demanded being greater than 
it is considered advisable to construct a single 
boiler to supply. In such cases it is usually 
important that they should be so set and con- 
nected that either or any of them may be 
a ||.g»itMm,§, operated separately. To secure this result, 
I il,^B^ir the connections with the feed and steam-pipes 
must be so made that it may be perfectly 
practicable to put the feed on either or any 
Upright Boiler of the boilcrs in the battery, and to take steam 
from either or any. Each should have its 
own separate safety-valve, check-valve, and steam-gauge. 

An upright boiler fitted with " Field tubes " is shown in Fig. 
26. The internal, cir- 
culating, tubes project 
slightly above the 
crown-sheet, and are 
carried down inside the 
main tube, nearly to 
the closed lower end. 
The water enters the 
centre tube, flows out 
at its lower end, and 

rises in the outer tube f.g. 27.-locomotive boiler. 

— on all sides the smaller one — issuing above the crown-sheet into 
the general body of v/ater, and there discharging the accompany- 
ing steam which had been made during the period of circulation. 
17. The Locomotive Boiler is always given a form sub- 
stantially as represented in Fig. 27, and consists of a firebox 
of rectangular form, attached to a cylindrical shell closely filled 




28 



THE STEAM-BOILER. 



with fire-tubes, through which the gases pass directly to the 
smoke-stack. Strength, compactness, great steaming capacity, 
fair economy, moderate cost, and convenience of combination 
with the running parts, are secured by the adoption of this 
form. It is frequently used also for portable and stationary 
engines. It was invented in France by M. Seguin, and in 
England by Booth, and used by George Stephenson at about 
the same time — 1828 or 1829. 




Fig. 28.— The Locomotive. Section. 



This form of steam-boiler has been found to lend itself with 
peculiar handiness to the special requirements of locomotive 
construction, and its use is universal for this purpose. 

18. The "Marine" Boilers are often of very different 
form from those used on land. They have assumed their 
present forms after many years of experience and slow adapta- 
tion to the special conditions by which they are controlled. 
When steam-pressures were customarily low, the controlling 
condition was the form of the vessel, and boilers were given 
such shapes as would permit of their being compactly stowed 
on board ship ; in the later days of very high pressure which 
have followed the introduction of the surface-condenser, and 
of high expansion, the form of the steam-generator is deter- 
mined mainly by the demand for their safe operation. 

Fig. 29 shows one of the types of boiler in most common 
use on the steamers generally seen on the Eastern American 
rivers, and on the coast, before the period of high steam and 
great economy had opened. 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 29 

It is known as the " Return-flue" boiler, the flame and 
gases from the furnace passing back to the " back-connection" 
through one set of flues, usually of 10 to 20 or even 24 inches 
in diameter, and thence to the " front-connection" over the 
furnace, and to the " uptake," and chimney or " smokestack," 
by a set of flues of, as a rule, smaller size and larger number. 
This is seen to be a " firebox boiler, no brickwork setting being 
admissible on shipboard. 




Fig. 29.— Flues and Return-tubes. 



Surrounding the chimney uptake is a reservoir, called the 
"steam-chimney," which answers the double purpose of a 
steam-dome and a drier, or " superheater," in which the steam 
may part with its suspended water, and often become heated 
above the temperature of saturation by the heat from the 
chimney gases. An elaborate system of bracing and staying 
is required for a boiler of this type. The sketch (Fig. 29) 
shows one of a pair of boilers arranged to discharge their flue 
gases into a common chimney. 

An effort ttr secure increased steaming capacity and 
economy in this boiler resulted in the production of the boiler 



30 



THE STEAM-BOILER. 



with direct flues and return-tubes, the latter being usually from 
three to five inches in diameter. This represents the later 
type, and one which is still very often used on paddle-steamers 
on Long Island Sound and on the rivers connected with that 
system of water communication. 

Fig. 30 illustrates a still more 
advanced type, the marine tubular 
boiler, extensively used in naval 
and other sea-going steamers, car- 
rying from twenty-five to forty 
pounds steam-pressure. The fur- 
nace discharges its gases directly 
into the back-connection, whence 
they pass forward into the front 
connection and stack through a 
set of tubes, which are commonly 
22" to i\ inches in diameter. This arrangement gives a 
very compact, well-proportioned boiler, comparatively easy 
of calculation and construction, and especially convenient in 
bracing and staying. Several furnaces can in this boiler be 
conveniently placed side by side and connected to a common 
uptake. 

19. The Marine Water-tube Boiler (Fig. 31) represents 
a type which has been often proposed for use at sea, but jvhich 
has never succeeded in finding its way into common use. 




Fig. 30.— Marine Tubular Boiler. 




Fig. 31.— Marine Water-tube Boiler. 



Lord Dundonald in Great Britain and James Montgomery 
in the United States introduced boilers of the water-tube 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 3 1 

type before the middle of the century, and the form here il- 
lustrated, as originally designed by Mr. Martin of the U. S. 
Navy, was very extensively employed on the vessels of the 
navy during the Civil War. In these boilers the gases pass 
from the back-connection to the front through a '' tube-box" 
placed in the water-space of the boiler, which tube-box con- 
tains a larg-e number of vertical tubes within which the water 
circulates from the lower to the upper side, while the gases 
pass among and around the tubes. 

These boilers were found by Isherwood to give a somewhat 
larger steaming capacity and greater economy also than the 
corresponding boiler of the fire-tube type; but the difficulty 
of repairing leaky tubes and incidental disadvantages, as well 
as their greater cost, prevented their permanent adoption in 
either the navy or the merchant service. 

20. The Scotch or Drum Boiler (Fig. 32) is the outcome 
of the attempt to secure a safe form of boiler for high pres- 





FiG. 32. — Scotch or Drum Boiler. 

sures, and it has, very naturally, assumed the cylindrical form 
of shell, while retaining the general disposition of furnace and 
tubes illustrated in the last-described fire-tube boiler. The 
furnaces are large, set in very thick flues ; the grates are set in 
them at very nearly the horizontal diametrical line, and, in the 
case illustrated, the boiler is " double-ended." Heavy stay- 
rods, connecting the two ends, make the heads capable of 
safely carrying their enormous loads. These boilers often 
carry 100 and 150 pounds pressure, and sometimes even more, 



32 



THE STEAM-BOILER. 



and are built of between lO and 20 feet diameter, and of iron 
or steel from f to i^ inches in thickness. 

Fig. 33 exhibits the method of setting and of connection 
of these boilers, as customarily practised where " single-ended," 
i.e., with the furnaces at one end only, as here seen. Either 
or any of these boilers, as so set, may be used or repaired sep- 
arately if necessary. 

For small powers these boilers are often given the form and 
structure shown in Fig. 31, which represents a boiler designed 
for a small yacht or a torpedo-boat ; it is three or four feet in 




Fig. 33. — Setting and Connection of Scotch Boilers. 



diameter and four to six feet long, and is calculated for from 
five to ten or twelve horse-power. 

21. Sectional Boilers are all constructed to meet the con- 
ditions and requirements so well stated by Col. Stevens in his 
specification for his British patent of 1805, in which he says 
that, to derive advantage from his principle, ^' it is absolutely 
necessary that the vessel or vessels for generating steam should 
have strength sufficient to withstand the great pressure from an 
increase of elasticity in the steam ; but this [total] pressure is 
increased or diminished in proportion to the capacity of the 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 33 

containing vessel. The principle, then, of this invention con- 
sists in forming a boiler by means of a system or combination 
of a number of small vessels, instead of using, as in the usual 
mode, one large one ; the relative strength of the materials of 
which these vessels are composed increasing in proportion to 
the diminution in capacity." 




Fig. 34. — Marine Boiler of Small Power. 



Stevens' boilers were of two kinds : the one that shown in 
Fig. 10; the other, and that specifically shown in the patent, 
consisting of systems of small tubes grouped in circular con- 
centric rows, and connected at each end by annular heads and 
chambers of sufficiently small capacity to be safe, while still 
large enough to permit good circulation. 

The boiler adopted in Gurney's steam-carriage (Fig. 1 1) is a 
later type, which has been more than once since reproduced; 
and nearly all recent, familiar, forms of the sectional boiler are 

3 



34 



THE STEAM-BOILER. 



constructed of systems of tubes united at the ends, and with 
the feed-apparatus, steam-drum, and mud-drum, by what are 
known as "headers," through which the general circulation is 
secured. In some cases the boiler has been made wholly or 
partly of cast-iron, as the early Babcock & Wilcox (Fig. 35), 
which consisted of a system of horizontal cast-iron tubes serv- 
ing both as water connections and 
as steam-chambers, and a second 
system of tubes set at a considera- 
ble inclination from the horizontal, 
the two sets united by headers. 

TJie Babcock & Wilcox Boiler ^ 
in the latest and best form, how- 
ever (Fig. 36), is wholly of wrought- 
iron or steel. The same general 
arrangement of tubes is preserved ; 
but the upper part of the construc- 
tion consists of one or more steam and water drums of com- 
paratively large diameter. These are away from the fire, and 
cannot be reached by the gases until they are cooled down to 
a safe temperature by passing through the lower system of 




Fig. 35.— Cast-iron Sectional Boiler. 




Fig. 36.— Babcock & Wilcox Boiler. 



heating surfaces, the inclined tubes. The water-line in the 
drum is carried at about its middle, and a dry-pipe, seen at the 
top, carries off the steam made. The joints are all '' milled," 
and so nicely fitted that no practicable pressure can cause leak- 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 35 

age. The course of the furnace gases and the water-circulation 
can be readily traced in the drawing. 

The Root Boiler is shown in Fig. 37, differing from the pre- 
ceding in the arrangement of tubes and their connection. The 
form of header is peculiar, and cannot be seen ; but the general 
construction is well shown in the engraving. In various 
designs, as made at different times and for various purposes, 
the construction has been somewhat modified, and the location, 




Fig. 37. — The Root Boiler, 



size, and number of steam-drums has been varied. The tubes 
are four or five inches in diameter, and usually eight or ten feet 
long. 

The Harrison Boiler (Fig. 38) consists of an aggregation of 
spheres, of cast-iron, or steel as now mxade, connected by 
^' necks" of somewhat smaller diameter. These spheres are 
8 inches in diameter, f inch thick, capable of sustaining a pres- 
sure exceeding 100 atmospheres, and are set in clusters, as 
shown in the sketch; they are fitted together with faced joints, 



36 



THE STEAM-BOILER, 



and secured by long bolts passing from end to end of each row. 
These boilers are intended to be so proportioned that a pres- 
sure far less than that which would produce rupture will 
stretch the bolts, thus allowing each joint to act as a safety- 




FiG. 38. — The Harrison Boiler, 



valve. The three types of boiler which have just been de- 
scribed, and their various modifications are the most common 
and familiar forms of sectional boiler in use. 

The Allen Boiler (Fig. 39) has only been constructed ex- 
perimentally, and has never come into the general market ; but 
experiments made upon it, under the direction of a committee 
of the American Institute, in 1871, and under the immediate 
direction of the Author, its chairman, gave excellent results, 
both in steaming capacity and economy. In this boiler the 
tubes are suspended by one end, the lower end being closed, as 
in what is known as the Field system. The inclination of the 
tubes 30° from the vertical was found by experiment to be best. 
The horizontal cylinders above, to one of which each line of 
tubes is connected, serve as circulating tubes and passages by 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 37 

which the steam made is conducted to the steam-drum. It 
will be noticed that the whole structure, steam-drum and all, is 
encased in the brick-work setting and exposed to contact with 
th.e heated gases. The circulation within the pendent tubes 
was excellent, and, with pure water and no sediment or in- 




FiG. 39. — The Allen Boiler. 



crustation choking them at their lower ends, the boiler was 
considered capable of doing its work in a very satisfactory 
manner. 

Fairbairn has remarked that '•' danger in the use of high- 
pressure steam does not consist in the intensity of the pressure 
to which the steam is raised, but in the character and construc- 
tion of the vessel which contains the dangerous element ;" and 
this remark may be taken, like the propositions of Col. John 



38 



THE STEAM-BOILER 



Stevens, as part of the basis of the philosophy of construction 
of "sectional" boilers. 

22. Marine Sectional Boilers have not as yet come into 
general use, although many attempts have been made to in- 
troduce them. The first boiler built by John Stevens was 
intended for use in a small steam-vessel; and in 1825 or 1826 
Robert L. Thurston and John Babcock, then of Portsmouth, 
and later of Providence, R. I., built boilers of this class, con- 
sisting of coils of pipe within which the water and steam were 
contained, the fire and furnace gases passing around outside 
them. Modifications of the Root boiler, known as the Belle- 
ville, and others, have been used with success by French build- 
ers of marine machinery; and the Babcock & Wilcox Co. have 
produced a marine boiler like that shown in Fig. 40, a com- 
bination of water-tubes below with fire-tubes and steam-space 
above, which is considered a good form for use at sea. 

The necessity of using a brick-work setting has prevented 

the introduction of the common 
forms at sea. Many designs are 
appearing constantly, and it is 
probably only a question of time, 
when, with continually rising 
steam-pressures, the older forms 
will be displaced by these modern 
and safer types. 

23. The Dates of Introduc- 
tion of the principal devices no- 
ticed in modern boilers have been 
given by Haswell, who describes 
the various familiar forms as in- 
cluding the dry-bridge and combustion-chamber of Wright 
(1756), Darrance (1845) ^^^^ Baker (1846); the dead-plate of 
Watt (1785); the water-bridge of Crampton (1842) and Mills 
(1851); the air-bridge of Slater (1831); the horizontal fire-tube 
of Bolton (1780), of Ericsson (1828), Seguin and Booth (1829), 
and of Hawthorne (1839) ^^^^ Glasson (1852); the vertical fire- 
tube of Rumsey (1788); the water-bottom of Allen (1730) and 
Fraser (1827) ; the vertical water-leg of Stephens and Hardle^ 




Fig. 40. — Babcock & Wilcox Marine 
Boiler. 



J/ISTuRY OF THE STEAM-BOILER— ITS STRUCTURE. 39 

(1748), Napier (1842) and Dundonald (1843); the steam-drum 
of John Stevens (1803); the superheaters of Hately (1768), of 
EngHsh (1809) and Allaire (who used a tall steam-chimney in 
1827). 

The hanging bridge of Johnson (18 18), the cylindrical 
return-flue boiler of Napier (1831), the cold-air supply above the 
fire, as by Thompson (1796), by Robertson (1800), Arnott 
(1821), and by Williams (1839), are also, he states, features of 
the modern boiler. The introduction of the water-tube boiler 
by Montgomery has not led to a change of type.^ 

These various details will be described more at length in 
later chapters. 

24. Peculiar and Special Forms of Boiler are met with 
in all departments. Some of these are considerably employed, 
and in many cases possess special features of advantage. The 




Fig. 41. — The Galloway Boiler. 

Galloway boiler (Figs. 41, 42) is one of the best known and suc- 
cessful modifications of the cylindrical flue-boiler. Its special 
feature is the conical stay-tube, which is used to increase the 
heating-surface and to strengthen the flue, without making the 
heating-surface difficult of access. Large numbers of these 
boilers have been built and used since about i860 in Great 
Britain, and some have been constructed in the United 
States. 



Trans. British Institution of Naval Architects, 187" 



40 



THE STEAM-BOILER. 



The exterior Is a plain cylindrical shell, within which are 
two cylindrical furnaces which unite in one flue, having parallel 




Fig. 42. — Galloway Boiler. 

curved top and bottom, struck from a centre below the boiler. 
In this flue are the conical 
water-tubes, each lo^ inches di- 
ameter at the top and 5-I inches 
diameter at the bottom, fixed in 
a radial position and perpen- 
dicular to the top and bottom 
so as to support and brace the 
flue and to intercept and break 
up the heated gases in their pas- 
sage from the furnaces. Along 
the sides of the flue there are 





Fig. 43.— Upright Flue- boiler. 



10 M 
Fig. 44.— Fire-engine Boiler. 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE. 4 1 

several wrought-iron pockets, or "bafflers," which deflect the 
currents and cause them to impinge against the tubes the 
end pocket providing for necessary expansion and contraction. 
After leaving this flue the gases pass along the sides of the 
shell to the front end, thence back again under the centre of 
the boiler to the chimney. 

A simple form of upright flue-boiler, for heating purposes 
and where small power is required, is seen in Fig. 43. It is 
of simple design, and easy of access for repair. 

A steam fire-engine boiler (Fig. 44), as built by the Silsby 




BOTTOM BLOW 



WWWNk^^ 



WWWNXW^ 



Fig. 45. — Herreshoff's Boiler. 



Co. illustrates the use of the Field tubes, pendent from the 
crown-sheet of the furnace: these are water-tubes, but the 
gases pass up through the boiler in a set of fire-tubes seen con- 
necting the crown-sheet with the top of the boiler. This makes 
an exceedingly compact, powerful, and light steam-boiler. 



42 THE STEAM-BOILER. 

The Herreshoff boiler (Fig. 45), as constructed for fast 
yachts and torpedo-boats, consists of a cone-shaped double 
coil of continuous wrought-iron pipe, five feet to five and a 
half feet in diameter, covered by a disk made up of a coil of 
smaller pipe. The feed-water passes through the latter, and 
downward through the boiler, inside, and then upward again,, 
through the outside coil, finally passing to the separator, 
whence the steam passes off to the engine, after circulating 
through the three top-coils of pipe which forms a super- 
heater, drying and superheating the steam en route. The 
water separated from the steam is driven back into the boiler, 
with the feed-water, by the feed and circulating pumps. The 
steam-pipe used in making up the boiler is lap-welded, and 
from if to 2f inches in diameter outside, and -f-^ inch in thick- 
ness. This boiler, as built for the yacht Leila, contained 22 
cubic feet of steam and water space, of which about one third 
was steam-space ; it had 485 square feet of heating-surface,. 
44 feet of superheating area, or 18.7 feet of heating-surface,, 
and 1.7 feet of superheating surface, per square foot of grate,, 
these areas being measured on the exterior of the tubes. The 
boiler developed 75 to 80 horse-power. The separator is 'ob- 
viously an essential feature of the system. 

25. Problems in Steam-boiler Design and Construction 
are among the most interesting, as well as important, which 
arise in the practice of the engineer. These problems may, 
and usually do, take many distinct forms. It is almost invari- 
ably the fact that the quantity of steam to be obtained is 
specified either as a certain weight of water to be evaporated 
and an equal weight of steam to be furnished; or a stated 
amount of power is to be given through a specified form and 
cize of engine, the probable efficiency of which is known or as- 
certainable ; or a stated volume of building, having a known 
exposure, is to be heated. In such cases the problem presented 
is to supply the steam so demanded at a minimum total cost, 
using a type of boiler to be selected with reference to the 
special conditions of location and use. 

It is often necessary, when dealing with a large " plant," to 
determine how many boilers should be employed, or to what 



HISTORY OF THE STEAM-BOILER— ITS STRUCTURE, 43 

extent the steam made should be divided up among them: 
whether a larger number of small boilers should be built or 
fewer large boilers. The selection of the best type for a speci- 
fied- location is an exceedingly common duty of the engineer. 
To secure the supply of a given quantity of steam with abso- 
lute safety, or with reasonable minimum risk, is another such 
problem. The usual case demands the production, with cer- 
tainty and with safety to life and property, of a stated weight 
of steam, day by day, for long periods of time, at minimum 
average total expense for the whole period of life of the 
boilers. 

Problems in construction, arising in connection with the 
design and application of steam-generators, are mainly related 
to the best methods of putting together the parts of a boiler 
of which the design has been made, and involve the continual 
application of a good knowledge of the nature and uses of the 
materials used, and especially of the facts and principles gov- 
erning the strength of materials, of parts, and of the structure as 
a whole. The selection of the best form of joint is a problem 
in the design of the boiler; but the determination of the best 
method of making that joint is a problem in construction. 
Such are all questions relating to the actual performance of 
work in the shop, the use of tools in the work of building the 
boiler, and the comparison of m.ethods. 

26. Problems in the Use of Steam-boilers are not less 
important and difficult of solution, often, than those which 
arise in the production of the design or in its construction. 
How to obtain a maximum quantity of steam ; how to secure 
dryness and uniformity of quality ; how to prolong the life of 
the structure ; and how to effect its preservation most effec- 
tively, at least cost in time, money, or loss of use — are only a 
few examples of the many problems that continually present 
themselves for immediate solution while the boiler is in ser- 
vice. 

27. The General Method of Solution of Problems in 
Design is to study the case very carefully in the light of all 
information that can be gained relating to the special conditions 
affecting it, and then, by comparison of the results of experi- 



44 THE STEAM-BOILER. 

ence with various boilers under as nearly as may be similar 
conditions, determining the best form for the case in hand. 
The designing engineer next endeavors to effect such improve- 
ment as his own talent and experience may enable him to 
originate, with a view to the most perfect possible adaptation 
of the design to its purposes. He next settles the general pro- 
portions, the forms of details, and finally the absolute dimen- 
sions and exact proportions. So much being done, he is pre- 
pared to make a preliminary study, which deliberately made 
alterations may convert into a finally complete design. 



CHAPTER II. 

MATERIALS — STRENGTH OF MATERIALS AND OF THE STRUC- 
TURE. 

28. The Quality of the Materials used in the construc- 
tion of steam-boilers must obviously be very carefully consid- 
ered. Not only is the steam-boiler expected to bear great 
strains and high pressures, but the terrible consequences which 
are liable to follow its rupture make it important that it should 
sustain its load and do its work with the most absolute safety 
attainable. The structure is exposed to greater variety of con- 
ditions tending to weaken it and to shorten its life than any 
other apparatus familiar to the engineer ; and the results of its 
failure are more certain to be disastrous to human life, as well 
as to property. All parts of the boiler are, while under heavy 
stress, exposed to continually changing temperatures, with, 
usually, occasional variations extending over two hundred or 
more degrees Fahrenheit. Nearly every part is liable to cor- 
rosion, often of a kind which is the more dangerous because 
very difficult to detect or to gauge. The boiler is very liable 
to be subjected to peculiarly severe stresses due to accidental 
circumstances and to excessive steam-pressure or to deficiency 
of water. 

The material needed for the purposes of the boiler-maker 
should for all these reasons be as strong, tough, and ductile 
as it can possibly be made. Of these qualities it is evident 
that ductility, capability of bearing violent alteration of form 
without fracture, is even more vitally essential than strength. 
A lack of tenacity can be met by using more metal, but noth- 
ing can make amends for brittleness. Good boiler-plate must 
possess great strength, and must combine with it great ductil- 
ity — must have high elastic and total " resilience," as such a 
combination is termed. 



46 THE STEAM-BOILER. 

The various parts of the boiler require their material to 
exhibit somewhat different special qualities : tubes must be 
tough enough to bear the '' upsetting" action of the " ex- 
pander" by which they are secured in the tube-sheets, and yet 
must be hard enough to sustain reasonably well the abrading 
effect of cinder-laden currents of gas ; flue-sheets and especially 
furnace-sheets must be hard, and capable of resisting both the 
mechanical wear and the corrosive action of the furnace-gases 
and their burden of coal, ash, and cinder, and must at the same 
time sustain safely the continual variation of temperature to 
which they are subjected by the alternate impact of flame and 
of cold air as the fires are worked. The " shell " of the t)oiler 
is less affected by such stresses ; but it nevertheless must meet 
with a greater variety of loading, in a greater number of direc- 
tions, than perhaps any other known iron structure ; every 
change of pressure within it, every alteration of temperature, 
every rise or fall of the water-line, produces a variation of the 
amount and direction of the stresses to which its metal and 
joints are exposed. Great tenacity combined with ductility is 
the essential characteristic of all material used in the construc- 
tion of steam-boilers. 

29. The Principles Relating to the Strength of Mate- 
rials of construction,* and other qualities useful in resisting 
the strains to which steam-boilers are subject, are very simple 
and, in the main, well established. 

The Resistance of Metal to rupture may be brought into 
play by either of several methods of stress, which have been 
thus divided by the Author : 

j Tensile : resisting pulling force. 
L,ongituaina ... 1 Coj^pression : resisting crushing force. 

T Shearing : resisting cutting across. 

Transverse .... J Bending : resisting cross breaking. 

( Torsional : resisting twisting stress. 

When a load is applied to any part of a structure or of a 
machine it causes a change of form, which may be very slight, 

* Abridged and adapted from Part II., Chapter IX., " Materials of Engineer- 
ing," by the Author. 



MATERIALS— STRENGTH OF THE STRUCTURE. 4/ 

but which always takes place, however small the load. This 
change of form is resisted by the internal molecular forces of 
the piece, i.e., by its cohesion. The change of form thus pro- 
duced is called strain, and the acting force is a stress. 

The Ultimate Strength of a piece is the maximum resist- 
ance under load — the greatest stress that can exist before rup- 
ture. The Proof Strength is the load applied to determine the 
value of the material tested when it is not intended that ob- 
servable deformation shall take place. It is usually equal, or 
nearly so, to the maximum elastic resistance of the piece. It 
is sometimes said that this load, long continued, will produce 
fracture ; but, as will be seen hereafter, this is not necessarily, 
even if ever, true. 

The Working Load is that which the piece is proportioned 
to bear. It is the load carried in ordinary w^orking, and is 
usually less than the proof load, and is always some fraction, 
determined by circumstances, of the ultimate strength. 

A Dead Load is applied without shock, and once applied 
remains unchanged, as, e.g., the weight of a bridge ; it produces 
a uniform stress. A Live Load is applied suddenly, and may 
produce a variable stress, as, e.g., by the passage of a railway 
train over a bridge. 

The Distortion of the strained piece is related to the load 
in a manner best indicated by strain-diagrams. Its value as 
a factor of the measure of shock-resisting power, or of resilience, 
is exhibited in a later article. It sllso has importance as indi- 
cating the ductile qualities of the metal. 

The Reduction of Area of Section under a breaking load is 
similarly indicative of the ductility of the material, and is to 
be noted in conjunction with the distortion. 

E.g., a considerable reduction of section with a smaller pro- 
portional extension would indicate a lack of homogeneousness, 
and that the piece had broken at the soft part of the bar. 
The greater the extension in proportion to the reduction 
of area in tension, the more uniform the character of the 
metal. 

Factors of Safety. — The ultimate strength, or maximum 
capacity for resisting stress, has a ratio to the maximum stress 



48 



THE STEAM-BOILER. 



due to the working load, which, although less in metal than in 
wooden or stone structures, is nevertheless made of consider- 
able magnitude in many cases. It is much greater under mov- 
ing than under steady '' dead " loads, and varies with the char- 
acter of the material used. For machinery it is usually 6 or 8 ; 
for structures erected by the civil engineer, from 4 to 6. The 
following may be taken as minimum values of this " factor of 
safety" for the metals : 



Matekial. 


Load, 


Shock. 




Dead. \ Live. 




Iron and steel, copper and 

other soft metals 

The brittle metals and alloys 


5 
4 


8 
7 


10 + 
10 to 15 


Ratio of ultimate 

strength to 

working load^ 



The Proof Strength usually exceeds the working load from 
50 per cent with tough metals, to 200 or 300 per cent where 
brittle materials are used. It should usually be below the elas- 
tic limit of the material. 

As this limit, with brittle materials, is often nearly equal to 
their ultimate strength, a set of factors of safety, based on the 
elastic limit, would differ much from those above given for 
ductile metals, but would be about the same for all brittle ma- 
terials, thus: 



Material. 


Load, 


Shock. 




Dead. 


Live. 




Ferrous and soft metals. , . . 
Brittle metals and alloys. . . 


2 

3 


4 
6 


6 
8 to 12 


Ratio of elastic 
Resistance to 
vv^orking load. 



The figure given for shock is to be taken as approximate, 
but used only when it is not practicable to calculate the energy 
of impact and the resilience of the piece meeting it, and thus 
to make an exact calculation of proportions. 

The Measure of Resistance to Strain is determined in form 



MATERIALS— STRENGTH OF THE STRUCTURE. 49 

by the character of the stress. By stress is here understood 
the force exerted, and by strain the change of form produced 
by it. 

. Tenacity is resistance to a pulling stress, and is measured 
by the resistance of a section, one unit in area, as in pounds 
or tons on the square inch, or in kilogrammes per square cen- 
timetre or square millimetre. Then if T represents the te- 
nacity and K is the section resisting rupture, the total load 
that can be sustained is, as a maximum, 

P^TK. (i) 

Compression is similarly measured, and if C be the maxi- 
mum resistance to crushing per unit of area, and K the section, 
the maximum load will be 

P=CK. . • , (2) 

Shearing is resisted by forces expressed in the same way, 
and the maximum shearing stress borne by any section is 

P=SK. (3) 

Bending Stresses are measured by moments expressed by 
the product of the bending effort into its lever-arm about the 
section strained, and if P is the resultant load, / the lever-arm^ 
and M the moment of resistance of the section considered, 

Pl=M. . (4) 

Torsional Stresses are also measured by the moment of the 
stress exerted, and the quantity of attacking and resisting mo- 
ments is expressed as in the last case. 

Elasticity is measured by the longitudinal force, which, act- 
ing on a unit of area of the resisting section, if elasticity were 
to remain unimpaired, would extend the piece to double its 
■original length. Within the limit at which elasticity is unim- 
paired, the variation of length is proportional to the force act- 
ing, and if E is the ''Modulus of Elasticity,'' or "Young's Mod- 
4 



50 THE STEAM-BOILER. 

ulus," / the length, and e the extension, P being the total load, 
and K the section, 

^ = 5-^ (5) 

PI 

' = EK-- ••••••• (6) 

The Coefficients entering into these several expressions for 
resistance of materials are often called Moduli, and the forms 
of the expressions in which they appear are deduced by the 
Theory of the Resistance of Materials, and the processes are 
given in detail in works on that subject. 

These moduli or coefficients, as will be seen, have values 
which are rarely the same in any two cases ; but vary not only 
with the kind of material, but with every variation, in the same 
substance, of structure, size, form, age, chemical composition 
or physical character, with every change of temperature, and 
even with the rate of distortion and method of action of the 
distorting force. Values for each familiar material, for a wide 
range of conditions, will be given in the following pages. 

When a piece of metal is subjected to stress exceeding its 
power of resistance for the moment, and gradually increasing 
up to the limit at which rupture takes place, it yields and be- 
comes distorted at a rate which has a definitely variable rela- 
tion to the magnitude of the distorting force ; this relation, aL 
though very similar for all metals of any one kind, differs 
greatly for different metals, and is subject to observable altera- 
tion by every measurable difference in chemical composition or 
in physical structure. 

Thus in Fig. 46 let this operation be represented by the 
several curves a, b, c, d, etc., the elevation of any point on the 
curve above the axis of abscissas, OX, being made proportional 
to the resistance to distortion of the piece, and to the equiva- 
lent distorting stress, at the instant when its distance from the 
left side of the diagram, or the axis of ordinates, OY, measures 
the coincident distortion. As drawn, the strain-diagram, a a', 
is such as would be made by a soft metal like tin or lead ; b b' 



MATERIALS— STRENGTH OF THE STRUCTURE. 



SI 



represents a harder, and c c' 2. still harder and stronger metal, 
as zinc and rolled copper. If the smallest divisions measure 
the per cent of extension horizontally, and 10,000 pounds per 
square inch (703 kilogrammes per square centimetre) vertically, 
d d' would fairly represent a hard iron, or a puddled or a 
''mild" steel; while //^ and ^^' would be strain-diagrams of 
hard and of very hard tool steels, respectively. 

The points marked e, e' , e" , etc., are the so-called " elastic 
limits,'' at which the rate of distortions more or less suddenly 
changes, and the elevation becomes more nearly equal to the 
permanent change of form, and at these points the resistance 
to further change increases much more slowly than before. 



Y 


^^' J' 




/^ 




^ 






y^ 




-^^ 




="F-==T 


--- — — ' Ti^ ' f 


%- 


^^'' tt 


-. i -=^ 


~rf 


1- 2-^ 




L'e^ 


r+ 


--/.- AM^ 




///M^^Mf^ 


^x-=— F-=E — - — "^—M'~~~~T 


Izf"-- it= 


'1 i i^z: T 


^K" 


="^-4^>^^-^-=rh===T?Nrr=N^- 



Fig. 46. — Strain-diagrams. 



This change of rate in increase in resistance continues until a 
maximum is reached, and, passing that point, the piece either 
breaks, as at /' and £"', or yields more and more easily until dis- 
tortion ceases, or until fracture takes place, and it becomes zero 
at the base-line, as at JT. 

Such curves have been called by the Author " Strain-dia- 
grams." 

If at any moment the stress producing distortion is relaxed, 
the piece recoils and continues this reversed distortion until, 
all load being taken off, the recoil ceases and the piece takes 
its " permanent set." This change is shown in the figure at 
y /'\ the gradual reduction of load and coincident partial res- 
toration of shape being represented by a succession of points 



52 THE STEAM-BOILER. 

forming the line f'f", each of which points has a position 
which is determined by the elastic resistance of the piece as 
now altered by the strain to which it has been subjected. The 
distance Of measures the permanent set, and the distance 
f" f" measures the recoil. 

The piece now has qualities which are quite different from 
those which distinguished it originally, and it may be regarded 
as a new specimen and as quite a different metal. Its strain- 
diagram now has its origin at f'\ and the piece being once 
more strained, its behavior will be represented by the curve 
f f ^^^ f ■, a- curve which often bears little resemblance to the 
original diagram 0,f,f. The new diagram shows an elastic 
limit at e^, and very much higher than the original limit e^. 
Had this experiment been performed at any other point along 
the line/"/', the same result would have followed. It thus be- 
comes evident that the strain-diagram is a curve of elastic 
limits, each point being at once representative of the resistance 
of the piece in a certain condition of distortion, and of its 
elastic limit as then strained. 

The ductile, non-ferrous metals, and iron and steel and the 
truly elastic substances, have this in common — that the effect 
of strain is to produce a change in the mode of resistance to 
stress, which results in the latter in the production of a new 
and elevated elastic limit, and in the former in the introduction 
of such a limit where none was observable before. 

It becomes necessary to distinguish these elastic limits in 
describing the behavior of strained metals, and, as will be seen 
subsequently, the elastic limits here described are under some 
conditions altered by strain, and we thus have another form of 
elastic limit to be defined by a special term. 

In this work the original elastic limit of the piece in its or- 
dinary state, as at e, e', e'\ etc., will be called either the Origi- 
nal or the Primitive, Elastic Limit, and the elastic limit cor- 
responding to any point in the strain-diagram produced by 
gradual, unintermitted strain will be called the Normal Elastic 
Limit for the given strain. It is seen that the diagram repre- 
senting this kind of strain is a Curve of Normal Elastic Limits. 

The elastic limit is often said to be that point at which a 



MATERIALS— STRENGTH OF THE STRUCTURE. 53 

permanent set takes place. As will be seen on studying actual 
strain-diagrams to be hereafter given, and which exhibit accu- 
rately the behavior of the metal under stress, there is no such 
point. The elastic limit referred to ordinarily, when the term 
is used, is that point within which recoil on removal of load is 
approximately equal to the elongation attained, and beyond 
which set becomes nearly equal to total elongation. 

It is seen that, within the elastic limit, sets and elongations 
are similarly proportional to the loads, that the same is true 
on any elastic line, and that loads and elongations are nearly 
proportional everywhere beyond the elastic limit, within a 
moderate range, although the total distortion then bears a far 
higher ratio to the load, while the sets become nearly equal to 
the total elongations. 

The behavior of metals under moving or "live" load and 
under shock is not the same as when gradually and steadily 
strained by a slowly applied or static stress. In the latter case 
the metal undergoes the changes illustrated by the strain- 
diagrams, until a point is reached at which equilibrium occurs 
between the applied load and resisting forces, and the body 
rests indefinitely, as under a permanent load, without other 
change occurring than such settlement of parts as will bring 
the whole structural resistance into play. 

When a freely moving body strikes upon the resisting 
piece, on the other hand, it only comes to rest when all its 
kinetic energy is taken up by the resisting piece; there is then 
an equality of vis viva expended and work done, which is ex- 
pressed thus: 

——= P^^=PmS\ (7) 

2g t/o 



in which expression W is the weight of the striking body, V 
its velocity, p the resisting force at any instant, p^ the mean 
resistance up to the point at which equilibrium occurs, and s is 
the distance through which resistance is met. 

As has been seen, the resistance may usually be taken as 
varying approximately with the ordinates of a parabola, the 




54 THE STEAM-BOILER, 

abscissas representing extensions. The mean resistance is, 
therefore, nearly two thirds the maximum, and 

= / pdx — p„^s = ^et = ae\ nearly, . . (8) 

where e is the extension, and t the maximum resistance at 
that extension, and a a constant. Brittle materials, like hard 
bronzes and brasses, have a straight line for their strain-dia- 
grams, and the coefiiicient becomes ^ instead of f , and 



(9) 



Resilience^ or Spring, is the work of resistance up to the 
elastic limit. This will be called Elastic Resilience. The mod- 
ulus of elasticity being known, the Modulus of Elastic Resili- 
ence is obtained by dividing half the square of the maximum 
elastic resistance by the modulus of elasticity, E, as above, and 
the work done to the *' primitive elastic limit" is obtained by 
multiplying this modulus of resilience by the volume of the 
bar."^ 

The total area of the diagram, measuring the total work 
done up to rupture, will be called a measure of Total or Ulti-^ 
mate Resilience. Mallett's Coefficient of Total Resilience is 
the half product of maximum resistance into total extension. 
It is correct for brittle substances and all cases in which the 
primitive elastic limit is found at the point of rupture. With 
tough materials, the coefficient is more nearly two thirds — 
and may be even greater where the metal is very ductile, as,, 
e.g., pure copper, tin, or lead. Unity of length and of section 
being taken, this coefficient is here called the Modulus of 
Resilience. 

When the energy of a striking body exceeds the total re- 
silience of the material, the piece will be broken. When the 

* Rankine and some other writers take this modulus as — instead of -— . 

E 2E 



MATERIALS— STRENGTH OF THE STRUCTURE. 55 

energy expended is less, the piece will be strained until the 
work done in resistance equals that energy, when the striking 
body will be brought to rest. 

. As the resistance is partly due to the inertia of the 
particles of the piece attacked, the strain-diagram area is 
always less than the real work of resistance, and at high ve- 
locities may be very considerably less, the difference being 
expended in the local deformation of that part of the piece 
at which the blow is received. In predicting the effect of a 
shock it is, therefore, necessary to know not only the energy 
stored in the moving mass and the method of variation of the 
resistance, but also the striking velocity. To meet a shock 
successfully, it is seen that resilience must be secured sufificient 
to take up the shock without rupture, or, if possible, without 
serious deformation. It is in most cases necessary to make 
the elastic resilience greater than the maximum energy of any 
attacking body. 

Moving Loads produce an effect intermediate between that 
due to static stress and that due to the shock of a freely mov- 
ing body acting by its inertia wholly; these cases are, there- 
fore, met in design by the use of a high factor of safety, as 
above. 

As is seen by a glance at the strain-diagram, //"(Fig. 46), the 
piece once strained has a higher elastic resilience than at first, 
and it is therefore safer against permanent distortion by mod- 
erate shocks, while the approach of permanent extension to a 
limit renders it less secure against shocks of such great inten- 
sity as to endanger the piece. 

When the shock is completely taken up, the piece recoils, 
as at e^^f'f'y until it settles at such a point on that line — as- 
suming the shock to have extended the piece to the point e"''^ 
— that the static resistance just equilibrates the static load. 
This point is usually reached after a series of vibrations on 
either side of it has occurred. With perfect elasticity, this 
point is at one half the maximum resistance, or elongation, 
attained. Thus we have 

/ pdx — ; (10) 

e/o 2g 



56 THE STEAM-BOILER. 

but/ varies 2.s A x within the elastic limit, which limit has now 
risen to some new point along the line of normal elastic limits, 
as e^. Taking the origin at the foot oi f"f'\ since the varia- 
tions of length along the line Ox are equal to the elongations 
and to the distances traversed as the load falls, and as stresses 
are now proportional to elongations, 

p^ax', W/i=Ws; and W=P;. . . (ii) 

when the resisting force is /, the elongations x, while /i and s 
are maximum fall and elongation, and P is the maximum 
resistance to the load at rest. Then 

r^pdx = a j xdx — -/ = Ws; /. s = . . (12) 

For a static load, if / is the elongation. 



W 
W= P= as'; .'. s' = —. 
' a 



Hence, 



J = *' ('3) 



and the extension and the corresponding stress due to the 
sudden application of a load are double those produced by a 
static load. 

Where the applied load is a pressure and not a weight, 
i.e., where considerable energy in a moving body is not to be 
absorbed, as in the action of steam in a steam-engine, the 
only increase of strain produced by a suddenly applied load is 
that produced by the inertia of such of those parts of the mass 
attacked as may have taken up motion and energy. 

30. Tenacity, Elasticity, Ductility, and Resilience are 
the four essential qualities of a good material for use in steam- 
boiler construction. In some cases,, the relative values of 



MATERIALS— STRENGTH OF THE STRUCTURE, 5/ 

these several properties are very different from that relation in 
others. For example : while boiler-iron or steel must have 
ductility, even if tenacity is sacrificed to some extent to secure 
it, machinery irons and steels should have a certain amount of 
rigidity, and tool-steel a minimum allowable hardness, as their 
leading characteristics ; and in all, the essential property being 
secured, as good a combination of all the other valuable prop- 
erties is sought as can possibly be obtained. 

The problem of proportioning parts to resist shock is seen 
to involve a determination of the energy, or '' living force," of 
the load at impact, and an adjustment of proportion of sec- 
tion and shape of piece attacked such that its work of elastic 
or of ultimate resilience, whichever is taken as the limit, shall 
exceed that energy in a proportion measured by the factor of 
safety adopted. For ordinary live loads and moderate impact, 
requiring no specially detailed consideration, the factors of 
safety already given, as based upon ultimate strength simply, 
are considered sufficient ; in all cases of doubt, or when heavy 
shock is anticipated, calculations of energy and resilience are 
necessary, and these demand a complete knowledge of the 
character, chemical, physical, and structural, of every piece 
involved, of its resilience and method of yielding under stress, 
and of every condition influencing the application of the at- 
tacking force — in other words, a complete knowledge of the 
material used, of the members constructed of it, and of the 
circumstances likely to bring about its failure. 

The form of such parts should usually be determined on 
the assumption that deformation may some time occur ; and 
such expedients as that of Hodgkinson in enlarging the sec- 
tion on the weaker side, as well as the adoption of a larger 
factor of safety based on ultimate strength, are advisable. 

31. The Chemical and Physical Characteristics of Iron 
determines the value of the metal for the purpose of the engi- 
neer in construction. The following set of strain-diagrams 
(Fig. 47) may be taken as representative of the behavior of 
good samples of the various grades of wrought-iron and of 
steel above described. 

The diagrams a a, b b, c c, are those of commercial irons of 



58 



THE STEAM-BOILER. 



good quality, soft, medium, and hard respectively, and all of 
high ductihty. The elastic limits of a and b differ greatly in 
position, and the irons themselves are characteristically differ- 
ent. The one is in a condition of initial internal strain which 
has weakened it against external stresses ; but that strain being 
relieved by flow under strain, the iron is finally found to be 
stronger than the second piece. 

It is evident that the first is less valuable than the second, 



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==J— ||T| -rre-rn — TT TTTTTTl rr"422i 






:/ : :: ::: ::-:: : : ::^^i': 




\q ^^' ,-'' 




50,000 \^ 1 — __,Ji:_J l_-L ^r . , , . . _, — L 


— =t"i n — 1 1 TT TTi — rrn" ^1^ 


' ^.__j___^____ __^ 




^' '■^ 




: :^ . > . :: ::,2: : 








co-oooi, >^ >^ M uJ-ri iHi^^Trml 


Ctti-- =F 1 


.^Z.__^ m____^^ 




I—-/. ±^^_i^i 




4:0.000 >:: .^-r^^i'.^- p=iii^ 
























:'W' : :]2r ;;="!: t: : : :: : m 








„., //^ xh^ ' J^ 




















/T^ 




10.000 /T"- 




tt - - - - - - - - - - - - - 




c 






1 i 




::: : ±:: : :__::__::-__:"r_T__: 



Elongation per Cent. 



10 20 

Fig. 47. — Strain-diagrams of Iron and Steel. 



however, under any stresses that occur within the usual limits 
of distortion ; the engineer would choose h as having a higher 
elastic limit and much greater elastic resilience. 

The "elasticity line," e' e' , shows the amount of spring and 
of set at the point at which it is taken, and gives a measure of 
the modulus of elasticity. The harder iron, d d, is probably 
actually a puddled steel, and has been made by balling up the 
sponge in the puddling furnace too early to permit complete 



MATERIALS— STRENGTH OF THE STRUCTURE. 59 

reduction of carbon. The gradual increase in strength, with in- 
crease of carbon, and rise of the elastic limit, are shown, as well 
as the coincident loss of ductiHty, in the diagrams, e^f^g, and 
//, which are those of steels containing from 0,35 to i per cent 
carbon ; e and f are the diagrams from excellent samples of the 
product of the open-hearth and pneumatic processes, and the 
stronger specimens are representatives of the average crucible 
steel. 

The increase of resilience within the elastic range is seen to 
be very great as the percentage of carbon is increased. 

The chemical composition of iron and steel determines the 
real character of any sample, although differences of physical 
character and of molecular structure often seriously modify the 
value of pieces into the composition of which they enter. 
With cast metal, where sound castings have been secured, the 
chemical constitution of the metal being known from analyses, 
the value of the metal for purposes of construction may be 
usually well judged ; and a comparison of the data given by 
the chemist with the specific gravity of the metal, will gener- 
ally be sufificient to determine its character with great exact- 
ness. Specifications for cast-iron or cast-steel may usually be 
safely so drawn as to make the acceptance of the material de- 
pendent upon accordance with specified formulas of composi- 
tion and density. 

Thus : A good, gray foundry iron, free from phosphorus 
and low in silicon, and having a density of 7.25 to 7.28, is, un- 
less containing some peculiar and unusual constituent in excess, 
a safe iron to use for all purposes demanding strength Wrought- 
iron and " mild " steels are, on the other hand, so greatly mod- 
ified by the processes of preparation in the mill, that actual 
test can only be safely depended upon to determine their value 
in construction. 

Statements of the strength of iron or steel are not of great 
value in any case, when the metal of which the strength or 
ductility is given is specified by its trade or generic name sim- 
ply without a statement of its precise chemical composition and 
physical character. Wrought-iron varies in composition and in 
structure to such an extent that, while the softest and purest 



6o THE STEAM-BOILER. 

varieties often have a tenacity of but about 40,000 pounds per 
square inch (2812 kilogrammes per square centimetre), some 
so-called wrought-irons (properly puddled steels) have been met 
with by the Author in the market having a tenacity of double 
that figure ; some samples extend 25 per cent before breaking, 
while others, with similar shape and size of test-piece are found 
nearly as brittle as cast-iron. 

Cast-iron varies in tenacity from as low as 10,000 pounds 
per square inch (703 kilogrammes per square centimetre) to 
more than 50,000 pounds (3515 kilogrammes per square centi- 
metre) ; while metals are sold under the name of " steel " hav- 
ing tenacities varying from that of wrought-iron up to over 100 
tons per square inch (15,746 kilogrammes per square centi- 
metre). 

In the examples of results of tests of iron and steel which 
will be hereafter given, therefore, the character of the metal 
tested will usually be exactly defined by its chemical composi- 
tion. 

In comparing the results of test with the chemical constitu- 
tion of the material, it will be found that, in general, elements 
which increase tenacity also decrease ductility and resilience. 

Thus : carbon increases strength up to a limit beyond which 
an excess begins to weaken it, as at the limit which separates 
steel from cast-iron ; but every addition of strength takes place 
at the sacrifice of that ductility which is an essential property 
of good iron. 

Phosphorus adds strength, as do manganese and other less 
common constituents ; but in each case a limit to increasing 
strength is reached, and in each case the increase of strength 
noted is accompanied by an equally or more noticeable loss of 
ductility. It sometimes happens, however, that the elastic re- 
silience increases, with addition of such elements, up to a limit ; 
which limit is, however, reached long before the increase of 
strength ceases. 

The influence of the most common hardening elements upon 
the valuable qualities of '' rail-steel " and similar metals has not 
been studied sufficiently to determine their precise effect and 
their modifying action as mutually reacting upon each other. 



MATERIALS— STRENGTH OF THE STRUCTURE. 6l 

The hardening elements most usually met with in iron and 
steel are carbon, silicon, manganese, and phosphorus. Dr. 
Dudley^ takes the effect of manganese, carbon, silicon, and 
phosphorus to be as the numbers 3, 5, 7|-, and 15, and reckons 
the sum of their effects in " phosphorus units" on this basis, 
allowing 0.05, 0.03, 0.02, and o.oi per cent respectively of these 
elements, taken in the order just given, as each equivalent to 
one unit. He concludes that the sum should not exceed 31 or 
32 in rails and other soft ingot-metals, this figure being obtained, 
as above, by adding together the phosphorus percentage, one 
half the silicon, one third the carbon, and one fifth the manga- 
nese. Taken singly, the limit for phosphorus is placed at a 
maximum of o.io per cent, silicon at 0.04, manganese at 0.30 or 
0.40, and for such metals, carbon at 0.25 to 0.30 per cent. 
Higher proportions make the material too brittle for rails and 
similar uses. For boiler-place these elements should be re- 
duced nearly one half. ^ 

Steels containing more carbon are still more carefully chosen 
v/ith a view to the avoidance of the loss of ductility due to the 
action of other elements in presence of carbon. 

Manganese steels, i.e., steels containing a high percentage 
of manganese, having but little carbon or other of the harden- 
ing elements, are found to have peculiar value for many purpo- 
ses of construction ; but their use must be carefully avoided in 
steam-boilers, or elsewhere, when exposed to great and rapid 
changes of temperature. 

The chemical composition of cast-iron will usually, and es- 
pecially if checked by a determination of density, serve well as 
a guide to the selection of iron of any specified character for use 
in construction ; yet it is always advisable to supplement the 
analysis by the determination of its physical characteristics as 
revealed by inspection and by test. The openness or closeness 
of grain, the shade of color, the depth of chill, and other prop- 
erties capable ot detection by the senses, are valuable guides to 
the experienced engineer. 

The same is true of all forms of ingot metal, whether worked 



^ 



* Trans. Am. Inst. Mining Engineers, vol. vii- 



62 THE STEAM-BOILER. 

or unworked. Steels are selected by visual inspection with 
great accuracy and certainty ; but the engineer usually desires to 
compare the chemist's analysis with the results of mechanical 
tests, as well as to obtain the judgment of the steel-maker who 
inspects the topped ingots. 

The products of the pneumatic and of the open-hearth pro- 
cesses are now customarily tested both by the chemist's and by 
physical tests. 

The influence of mechanical treatment during the process 
of manufacturing wrought-iron and puddled steel — the "weld " 
metals — is very great in the modification of their valuable 
properties. This is the case to such an extent that the quality 
of these materials can but rarely be safely judged from chemi- 
cal analysis. The presence or absence of cinder, the amount of 
reduction in the rolls or under the hammer, and the tempera- 
ture and other conditions of working are circumstances that 
modify quality to such an extent as usually, with the better 
kinds of metal, to entirely obscure variations due to accidental 
differences in chemical constitution ; with other irons and steels 
both sets of conditions concur to determine quality. It is never 
safe, therefore, to base specifications for these materials upon 
chemical composition alone ; actual test is usually demanded as 
a basis for their acceptance or rejection. 

Cast-iron has some advantages as a material for steam-boil- 
ers, such as its durability in presence of corroding elements, its 
freedom from liability to rapid solution by acids, its compact 
structure and the impossibility of becoming laminated ; and it 
is found to have practically equal conducting power. Its cost 
is also low ; but it is exposed to danger of cracking, either from 
shrinkage strains or local variations of temperature ; it gives no 
warning when such danger arises, but is always treacherous and 
unreliable. Its composition is a matter of uncertainty, and is 
never absolutely know^n. The cast-iron boilers are usually so 
constructed that it is easy to substitute a new piece for a broken 
part, and the boiler is then as good as when new, instead of 
being weakened by the operation, as is apt to be the case with 
wrought-iron boilers. On the other hand, they are considered 
to be commonly somewhat defective in circulation, as a rule, 



MATERIALS— STRENGTH OF THE STRUCTURE. 63 

and deficient in steam-space. Cast-steel is now often substi- 
tuted for cast-iron in such boilers, and is at once stronger and 
more trustworthy ; it is subject to the same objection as cast- 
iron in the difficulty met with in securing sound castings. 
Could good castings be relied upon and shrinkage cracks and 
strain cracks be prevented, the material would undoubtedly be 
much more generally employed, especially in small boilers. 

32. Steel for Boilers is always of the class known as " low," 
*' soft," or '' mild " steel, and is, properly speaking, '' ingot iron ;" 
all of its characteristics being those of a homogeneous, tena- 
cious, and ductile iron, and quite distinct from those of the 
true steels. As compared with iron, its greater tenacity, per- 
mitting the use of thinner sheets for a given pressure, or giving 
a greater margin of safety; its greater homogeneousness, in- 
suring more certainty and security in attaining the conditions 
prescribed in designing; and its greater ductility, which adds 
enormously to the safety of the structure against dangerous 
strains and alterations of form : all make it, when of good qual- 
ity, much the more desirable material. It is rapidly supersed- 
ing iron in boiler-construction. The difficulties which have 
retarded its introduction have been mainly those of getting 
perfect uniformity of composition, not only in successive lots, 
but also in different parts of the same lot, and even in the same 
sheet. Many manufacturers have now become able to secure 
all the uniformity desirable, and to guarantee the quality of 
their product ; from them good boiler-plate can always be ob- 
tained. 

Steel boiler-plate is usually made by the Siemens-Martin or 
** open-hearth" process; although considerable quantities are 
produced from the Bessemer converter, and some by the more 
costly crucible process. The former possesses peculiar advan- 
tages in the making of " mild " steels and boiler-plate in conse- 
quence of the facility which it offers for testing the quality of 
the metal from time to time, while still molten on the furnace- 
hearth, and then, if it proves not to be of the desired character, 
modifying it, by addition of such material as may serve to im- 
prove it, until the required quality is obtained. While the 
Bessemer process in skilled hands has produced most excellent 



64 THE STEAM-BOILER. 

steel, very uniform in grade, neither it nor the crucible process 
offers such facilities for test and adjustment of quality as 
characterize the Siemens-Martin system. 

The composition of good steel boiler-plate should always 
be such as will give great ductility and perfect freedom from 
liability to harden and " take a temper" in consequence of 
variations of temperature occurring while in use. The carbon 
should be less in amount than one fourth of one per cent, and 
it is often less than one tenth. Manganese, which usually con- 
stitutes an important element, should be as low as is possible 
consistent with soundness arid homogeneousness. Any boiler- 
plate that, on being heated to a red-heat and suddenly cooled, 
is found to harden perceptibly, should be rejected. It should 
weld readily, and should be capable of sustaining all the tests 
customarily demanded of boiler-iron even more satisfactorily 
than the latter. Its ductility should be greater than that of 
iron. 

As ordinarily made, steel is rarely as easily manipulated, and, 
when subjected to the ordinary operations of boiler-making, 
seldom exhibits as little loss of quality as the best irons ; it 
must often be very carefully treated, and even in many cases 
must be annealed after each operation to restore lost ductility. 
Shearing and punching steels too high in carbon, or containing 
too much manganese or phosphorus, is very certain to produce 
injury. 

33. The Effect of Variation of Form of a piece of metal, 
a member, or a structure, is often extremely important. This 
generally so considerably modifies the apparent tenacity of 
iron and steel that it is necessary to note the size and shape 
of the specimen tested before an intelligent understanding of 
the value of the material can be arrived at by examination of 
data secured by test. When a piece of metal is subjected to 
stress and slowly pulled asunder, it will yield at the weakest 
section first ; and if that section is of considerably less area than 
adjacent parts (Fig. 48), or if the metal is not ductile, it will 
often break sharply, and without stretching appreciably, as seen 
in Fig. 50 ; the fractured surface will have a granular appearance, 
and the behavior of the piece, as a whole, may be like that of a 



MATERIALS— STRENGTH OF THE STRUCTURE. 



65 



brittle casting, even although actually made of tough and duc- 
tile metal, when the piece is deeply scored. 

When a bar of very ductile metal, of perfectly uniform cross- 
section (Fig. 49) is broken, on the other hand, it will, at first, if 
of uniform quality, gradually stretch with a nearly uniform 
reduction of section from end to end. Toward the ends, where 
held by the machine, this reduction of area is less perceivable, 
and on the extreme ends, where no strain can occur, except from 
the compressing action of the grips, the original area of sectioa 



ZN, 




Fig. 48. — Incorrect. Fig. 49.— Correct. 

Forms of Test-pieces for Tension. 



is retained, diminution taking place from that point to the most 
strained part by a gradual taper or by a sudden reduction of 
section, according to the method adopted of holding the rod. 
When the stress has attained so great an intensity that the 
weakest section is strained beyond its elastic limit, '' flow " 
begins there, and, while the extension of other parts continues 
slowly, the portions immediately adjacent to the overstrained 
section stretch more and more rapidly as this local reduction 
of section continues, and finally fracture takes place. This 
locally reduced portion of the rod has a length which is depend- 
ent upon the character of the metal and the size of the piece. 
5 



66 



THE STEAM-BOILER. 



Hard and brittle materials exhibit very little reduction, and 
the reduced portion is short, as in Fig. 50 : 
ductile and tough metals exhibit a marked re- 
duction over a length of several diameters, and 
great reduction at the fractured section, as seen 
in Fig. 51. Of the samples shown in the figures, 
the first is of a good, but a badly worked, iron, 
and the second from the same metal after it 
had been more thoroughly worked. 

When the breaking section is determined by 
deeply grooving the test-piece, the results of test 
are higher by 5 or 10 per cent than when the 
cylinders are not so cut, if the metal is hard and 
brittle, and by 20 to 25 per cent with tough 
and ductile irons or steels. In 
ordinary work this difference will 
average at least 20 per cent with 
the ductile metals. A good 
bridge or cable iron in pieces of 
I inch (2.54 centimetres) diame- 
ter cut from 2-inch (5.08 centi- 
exhibited a tenacity of 50,000 
pounds per square inch in long test-pieces, 
and 60,000 in short grooved specimens (3515 
to 4218 kilogrammes per square centimetre). 
Cast-irons will give practically equal results by 
both tests, as will hard steels and very coarse- 
grained hard wrought irons. 

Since these differences are so great that it 
is necessary to ascertain the form of samples 
tested before the results of test can be properly 
interpreted, it becomes advisable to use a test- 
piece of standard shape and size for all tests the 
results of which are to be compared. The fig- 
ures given hereafter, when not otherwise stated, 
may be assumed to apply to pieces of one half 
square inch area (3.23 square centimetres) of Fig. 51. 

section, and at least 5 diameters in length. This length is 




Fig. 50. 

metres) bar 



MATERIALS— STRENGTH OF THE STRUCTURE. 6/ 

usually quite sufficient, and is taken by the Author as a mini- 
mum. For other lengths, the extension is measured by a con- 
stant function of the total length plus a function of the diame- 
ter, 'which varies with the quality of the metal and the shape 
of the test-piece. It may be expressed by the formula 

e^al^M) (I) 

The elongation often increases from 20 up to 40 per cent 
as the test-piece is shortened from 5 inches (12.7 centimetres) 
to \ inch (1.27 centimetres) in length, while the contraction of 
section is, on the other hand, decreased from 50 down to 25 per 
cent, nearly. Fairbairn,* testing good round bar-iron, found 
that the extension for lengths varying from 10 inches (25.4 
centimetres) to 10 feet (3.28 metres) could be expressed, for 
such iron, by the formula 






.(2) 



where / is the length of bar in inches. In metric measures this 
becomes 



/== length in centimetres; e = elongation per unit of length. 

This influence of form is as important in testing soft steels as 
in working on iron. Col. Wilmot, testing Bessemer "steel" at 
the Woolwich Arsenal, G. B., obtained the following figures: 

Tenacity. 

Form. Test-piece. Lbs. per sq. in. Kilogs. per sq. cm. 

Grooved, Fig. 48, Highest 162,974 ii,457 

Lowest 136,490 9,595 

Average.... 153,677 10,803 

Long cylinder Highest 123,165 8,658 

Lowest 103,255 7-259 

Average 114,460 8,047 

* Useful Information, second series, p. 301. 



68 



THE STEAM-BOILER. 



The difference amounts to between 30 and 35 per cent, the 
groove giving an abnormally high figure. 

It is evident from the above that the elongation must be 
proportionably much greater in short specimens than in long 
pieces. This is well shown below in tests made by Capt. 
Beardslee for the United States Board.* 





TESTS OF TEST-PIECES 


OF VARYING 


PROPORTIONS— TENSION. 






k 








Stress when 










Length. 


be 

c 



Diame- 


2 


Piece began 


Breaking- 






ter. 


G ■ 


TO stretch 


stress. 

















observably. 


























Remarks. 


a 


Orig- 
inal. 


Final. 


G 
?.0 


13 

c 


3 


c 


Ob- 
served 


Stress 
per 


Ob- 
served 


Stress 
per 









In. 


In. 


^'"^ 


Stress. 


inch. 


Stress. 


inch. 






In. 


In. 


Lds. 


Lis. 


Lds. 


Lbs. 




I 


5.000 


6.522 


30.0 


.798 


.568 


49-3 


13,400 


26,800 


26,000 


51,989 


Elastic limit, 26,795 lbs. 




























per sq. in. 


2 


3-938 


5.204 


32.0 




798 


.564 


50 





14,000 


28,000 


26,200 


52,389 


Elastic limit, 28,194 lbs. 
per sq. in. 


3 


4.500 


5-853 


30.0 




797 


.584 


46 


' 


14,000 


28,290 


26,190 


52,495 


Elastic limit, 28,062 lbs. 
per sq. in. 


4 


3.500 


4.605 


31.6 




791 


.570 


48 





13,000 


26.450 


26,070 


53.052 


Elastic limit, 27,268 lbs. 
per sq. in. 


5 


• 3.000 


3-977 


33.0 




792 


•571 


48 





14.000 


28,420 


26,100 


52.984 




6 


2.472 


3.266 


32.1 




799 


.589 


45 


6 


14,000 


27,920 


26,500 


52,852 




7 


1.989 


2.644 


32.9 




798 


.591 


45 





14,000 


28,000 


26,500 


53,169 




8 


1.500 


2.026 


35.0 




797 


.590 


45 


2 


15,500 


31,320 


26,275 


52,666 




9 


1. 000 


1-354 


35.4 




798 


.600 


43 


5 


16,675 


33,350 


26,590 


53,169 




10 


0.500 


0.708 


41.6 




798 


■635 


36 


6 


18,760 


37,520 


28,665 


57,3^8 





With such brittle materials as the cast-irons, the difference 
becomes unimportant. Beardslee found a difference of but i 
per cent in certain cases. The more brittle the material the less 
this variation of the observed tenacity. 

As will be seen later, even more important variations follow 
changes of proportion of pieces in compression. No test-piece 
should be of very small diameter, as inaccuracy is more 
probable with a small than with a large piece, and the errors 
are more likely to be increased in reduction to the stress per 
square inch. The length should not be less than four times the 
diameter in any case, and with soft ductile metal five or six 
diameters would be preferable, for tension. 



* Report, p. 104. 



MATERIALS— STRENGTH OF THE STRUCTURE. 69 

Where much work is to be done, it is quite important that 
a set of standard shapes of test-pieces should be selected, and 
that all the tests should be made upon samples worked to 
standard size and form. Thus, tension-pieces are often made 
of the shapes seen in the figure, when testing square, cylindrical, 
or flat samples, or samples cut from the solid. The last is a 
shape called for under the U. S. inspection laws when testing 
boiler-plate ; but it should never be used if choice is permitted, 
as it gives no chance of stretching, and is therefore nearly use- 
less as a gauge of the quality of the metal ; it will undoubtedly 
be abandoned in course of time, as it invariably gives too high a 
figure, and does not distinguish the hard and brittle from the 
better and tougher materials which are desired in construction. 

The dimensions adopted by the Author are one-half square 
inch (3.23 square centimetres) section for all metals except the 

„ 16 "to sol » 

ie"T020l 

I6"tOZO"_ 

.ig'tozo'. 
8''ro /2I » 



Fig. 52. — Shapes for Test-pieces. 



tool steels (0.798 inch; 2 centimetres diameter when round), 
and one-eighth or one-quarter square inch (0.81 to 1.61 square 
centimetres area; 0.398 or 0.565 inch, i or 1.4 centimetres diame- 
ter) for the latter, at the smallest cross-section. Kent, who sketches 
the above, takes these shapes, making them, if of tool steel, fl- 
inch diameter (1.75 centimetres), or | square inch (2.44 square 
centimetres) area ; in other metals either | inch (1.9 centimetres) 



JO 771 £ STEAM-BOILER. 

diameter or 0.44 square inch (2.84 square centimetres), or as 
above. The edges should be true and smooth, and the fillets ^ 
inch radius. 

For compression tests of metal, 1 inch (2.54 centimetres) 
long and \ inch (1.27 centimetres) diameter, ends perfectly 
square, is recommended ; for stone and brick, a 2-inch (5.08 
centimetres) cube. Transv^erse test-pieces should not be less 
than I foot nor more than 4 feet in length, when to be handled 
in ordinary machines. 

The standard specimen will be taken as above, and good 
wTought-iron of such shape and size should exhibit a tenacity 
of at least 50,000 pounds (3515 kilograms per square centimetre) 
if from bars not exceeding 2 inches (5.08 centimetres) diameter, 
and should stretch 25 per cent with 40 per cent reduction of 
area. Such test-pieces have the advantage of giving uniform 
comparable and minimum figures for tenacity, and of permitting 
accurate determinations of elongation. 

Test-pieces are only satisfactoiy in form when turned in 
the lathe, as the coincidence of the central line of figure with 
the line of pull is thus most perfectly insured. When, as w^ith 
sheet-metal, this cannot be done readily, care must be taken to 
secure proportions of length and cross-section as nearly like 
those of the standard test-piece as possible, and to secure sym- 
metry and exactness of form and dimension ; such pieces are 
liable to yield by tearing when not well made and properly 
adjusted in the machine. 

34. The Method of Treatment of metal, either previous 
to its use in any structure or while under load, often seriously 
modifies its strength, its ductility, and its endurance. 

Bar-irons exhibit a wide difference of strength, due to 
difference of section alone. This variation may be expressed 
approximately with good irons, such as the Author has studied 
in this relation, by the formulas 

T — 56,000 — 20,000 log d\ \ , 

T„,— 4' 500— 1,406 log ^^.) ' ' ' ' \^ 

Where T and T„i measure the tenacity in British and metric 



MATERIALS— STRENGTH OF THE STRUCTURE. 



measures respectively, and d and d„i the diameter of the piece, 
or its least dimension. 

Where it is desired to use an expression which is not loga- 
rithmic, it will usually be safe to adopt in specifications the 
following: 



T — -^^^^^ T — ^^>^^^ 



(2) 



The Edgemoor Iron Company adopt, for wrought-iron in 
tension, the formula 



T = 52,000 



7,000^ 



in which A is the area, and B the periphery of the section.* 

The figures in the following table have been taken by the 
Author as fair values of the tenacity of good average merchant- 
iron. 



TENACITY OF GOOD IRON. 



Diameter. 


Tenacity, T. 


Centimetres. 


Inches. 


Lbs. 
per square inch. 


Kilogrammes 
per square inch. 


.64 


i 


60,000 


4.218 


1.27 


i 


■ 58,000 


4,077 


1 .90 


f 


56,000 


3947 


2.54 


I 


55.500 


3,902 


3.18 


li 


54,500 


3.838 


3.81 


li 


53,500 


3,761 


4-45 


If 


52.000 


3,656 


5.08 


2 


50,000 


3.515 


5.72 


2ir 


49,000 


3-445 


6.35 


2i 


48,900 


3-374 


7.62 


3 


47.500 


3.320 


8.90 


3* 


47,000 


3,304 


10.16 


4 


46,000 


3.234 


12.70 


5 


44,000 


3.093 



Kirkaldyf found that pieces of ij-inch (3.2 centimetres) 

* Ohio Railway Report. 1881, p. 379. 

f Experiments on Wrought Iron and Steel. 



72 THE STEAM-BOILER. 

bar rolled down to i inch (2.54 centimetres), f inch (1.9 centi- 
metres), and \ inch (1.27 centimetres) diameter increased in 
tenacity 20 per cent while decreasing in ductility 5 per cent. 

Forging has the same effect as rolling. 

The elastic limit is also usually lower in large than in small 
masses. 

Turning iron down has no important effect on the tenacity. 
The considerable variations always observable in the gen- 
eral rate of increase of tenacity, which, other things being 
equal, accompanies reduction of size of wire, are due to the 
hardening of the wire in the draw-plate, and occasional restora- 
tion to its softest condition by annealing. 

Beardslee has found the change of tenacity in forged and 
rolled bars to be due to differences in amount of work done in 
the mill upon the iron. The extent of reduction of the pile 
sent to the rolls from the heating-furnace is variable, its cross- 
sectional area being originally from 20 to 60 times that of the 
bar, the higher figure being that for the smallest bars. On 
making this reduction uniform, it is found that the tenac- 
ity of bars varies much less in different sizes, and that the 
change becomes nearly uniform from end to end of the series 
of sizes, and becomes also very small in amount. By properly 
shaping the piles at the heating-furnace, and by putting as 
much work on large as on small bars, it was found that a 2-inch 
(5.08 centimetres) bar could be given a strength superior by 
over 10 per cent, and a 4-inch (10.17 centimetres) could be 
made stronger by above 20 per cent than iron of those sizes as 
usually made for the market. The surface of a bar is usually 
somewhat stronger than the interior. 

The Limit of Elasticity will be found at from two fifths 
the ultimate strength in soft, pure irons to three fifths in 
harder irons, and from three fifths in the steels to nearly the 
ultimate strength with harder steels and cast-irons. Barlow 
found good wrought-iron to elongate one ten-thousandth its 
length per ton per square inch up to the limit at about 10 
tons. The relation between the series of elastic limits and the 
maximum resistance of the iron or the steel is well shown in 
strain-diagrams, which exhibit graphically the varying relation 



MATERIALS— STRENGTH OF THE STRUCTURE. 73 

of the stress applied to the strain produced by it throughout 
the process of breaking. 

Repeatedly Piling and Reworking improves the quaHty of 
wrought-iron up to a limit at which injury is done by over- 
working and burning it. 

The iron thus treated exhibits increasing strength until it 
has been reheated five or six times, and then gradually loses 
tenacity at a rate which seems to be an accelerating one. 
Forging iron is similar in effect, and improves the metal up to 
a limit seldom reached in small masses. 

The forging of large masses usually includes too often re- 
peated piling and welding of smaller pieces, and it is thence 
found difficult to secure soundness and strength. This is par- 
ticularly the case where the forging is done with hammers of 
insufficient weight. The iron suffers, not only from reheating, 
but from the gradual loosening and weakening of the cohesion 
of the metal within the mass at depths at which the beneficial 
effect of the hammer is not felt. 

The Effect of Prolonged Heating is sometimes seen in a 
granular, or even crystalline, structure of the iron, which indi- 
cates serious loss of tenacity. Large masses must always be 
made with great care, and used with caution and with a high 
factor of safety. Ingot iron is always to be preferred to welded 
masses of forged material for shafts of steamers and similar 
uses. 

The Tenacity of Ingot Irons and Steels is less subject to 
variation by accidental modifications of structure and compo- 
sition than is that of wrought-iron. The steels are usually 
homogeneous and well worked, and are comparatively free 
from objectionable elements, their variation in quality being 
determined principally by the amount of carbon present, which 
element occurs in a proportion fixed by the maker, and varying 
within a very narrow range. The softest grades of ingot iron 
and steel approach the character of wrought-irons ; but their 
comparative freedom from slag, and their purity, usually make 
them superior to all ordinary irons in combined strength and 
ductility. The products of the Bessemer and of the open- 
hearth processes vary in tenacity from 6o,ooo pounds per square 



74 THE STEAM-BOILER. 

inch (4218 kilogrammes per square centimetre) to more than 
double that figure ; while the crucible steels often, and occa- 
sionally the preceding, are sometimes four times as strong, a 
tenacity of 200,000 pounds per square inch (14,060 kilogrammes 
per square centimetre) being sometimes exceeded. 

35. The Time and the Margin of Stress, or loading, 
both affect greatly the life of the piece and the degree of safety 
with which it may be used. 

It has been shown by the Author, and by Commander 
Beardslee, U. S. N., by direct experiment in the Mechanical 
Laboratory of the Stevens Institute of Technology, and at the 
Washington Navy Yard, that the normal elastic limit, as ex- 
hibited on strain-diagrams of tests conducted without inter- 
mission of stress, is exalted or depressed when intermission of 
distortion occurs, according as the metal belongs to the iron or 
to the tin class. This elevation of the normal elastic limit by 
intermitting strain is, as has been shown, variable in amount 
with different materials of the iron class, and the rate at which 
this exaltation progresses is also variable. With the same 
material and under the same conditions of manufacture and of 
subsequent treatment the rate of exaltation is quite definite, 
and may be expressed by a very simple formula. The Author 
has experimented with bridge material, and Commander 
Beardslee has examined metal specially adapted for use in 
chain cables, for which latter purpose an iron is required, as in 
bridge-building, to be tough as well as strong and uniform in 
structure and composition. The experiments of the latter in- 
vestigator have extended to a wider range than have those of 
the Author, and the effect of the intermission of strains con- 
siderably exceeding the primitive elastic limit has been deter- 
mined by him for periods of from one minute to one year. 
From a study of the results of such researches and from a com- 
parison with the latter investigation, which was found to be 
confirmatory of the deduction, the Author has found that, with 
such iron as is here described, the process of exaltation of the 
normal elastic limit due to any given degree of strain usually 
nearly reaches a maximum in the course of a few days of rest 
after strain, its progress being rapid at first and the rate of in- 



MATERIALS— STRENGTH OF THE STRUCTURE. 



n 



crease quickly diminishing with time. For good boiler irons, 
the amount of the excess of the exalted limit, as shown by sub- 
sequent test, above the stress at which the load had been pre- 
viously removed may be expressed approximately by the 
formula 

E' = ^ log T-\- 1.50 per cent ; 

in which the time, T, is given in hours of rest after removal of 
the tensile stress which produced the noted stretch. 

The Author has investigated the action of prolonged stress, 
using wire of Swedish iron : but one set of samples was an- 
nealed ; the other, of two sets, was left hard, as drawn from the 
wire-blocks. The size selected was No. 36, 0.004 inch (0.0 1 
millimetre) diameter, and was loaded with 95, 90, 85, 80, 75, 
70, 65, and 60 per cent of the breaking load as obtained by the 
usual method of test. The result was: 



ENDURANCE OF IRON WIRE UNDER STATIC LOAD. 


Per Cent Maximum 


Time under Load 


BEFORE Fracture. 


Static Load 


Hard wire (unannealed). 


Soft wire (annealed). 


95 
90 

85 
80 

75 
70 

65 
60 


8 days. 

35 c^ays. 

Unbroken at end of 16 mos, 

91 days. 

>• Unbroken. 

Unbroken. 


3 minutes. 
5 minutes. 

I day. 

266 days. 

17 days. 

455 days. 

455 days. 

Several years. 



Soft irons and the " tin class" of metals and the woods are 
found to demand a higher factor of safety than hard iron. The 
elegant and valuable researches, also, of Mons. H. Tresca on 
the flow of solids,"^ and the illustrations of this action almost 
daily noticed by every engineer, seem to lend confirmation to 
the supposition of Vicat. The experimental researches of 
Prof. Joseph Henry, on the viscosity of materials, and which 



Sur I'Ecoulement des corps solides. Paris, 1869-72. 



76 THE STEAM-BOTLER. 

proved the possibility of the coexistence of strong cohesive 
forces with great fluidity,* long ago proved also the possibility 
of a behavior in solids, under the action of great force, analo- 
gous to that noted in more fluid substances. 

On the other hand, the researches of the Author, indicating 
by strain-diagrams that the progress of this flow is often ac- 
companied by increasing resistance, and the corroboratory evi- 
dence furnished by all such carefully made experiments on 
tensile resistance as those of King and Rodman, Kirkaldy and 
Styffe, have made it appear extremely doubtful whether hard 
iron is ever weakened by a continuance of any stress not origi- 
nally capable of producing incipient rupture. 

Kirkaldy concludes that the additional time occupied in 
testing certain specimens of which he determined the elonga- 
tion "had no injurious effect in lessening the amount of break- 
ing strain." f An examination of his tables shows those bars 
which were longest under strain to have had highest average 
resistance. 

Wertheim supposed that greater resistance was offered to 
rapidly than to slowly produced rupture. 

The experiments of the Author prove that, as had already 
been indicated by Kirkaldy, a lower resistance is offered by 
ordinary irons as the stress is more rapidly applied. This effect 
conspires with vis viva to produce rupture. 

We conclude that the rapidity of action in cases of shock, 
and where materials sustain live loads, is a very important ele- 
ment in the determination of their resisting power, not only 
for the reason given already, but because the more rapidly 
common iron is ruptured the less is its resistance to fracture. 
This loss of resistance is about 15 per cent :f in some cases, 
noted by the Author, of moderately rapid distortion. 

The cause of this action bears a close relation to that 
operating to produce the opposite phenomenon of the ele- 
vation of the elastic limit by prolonged stress, to be de- 

* Proc. Am. Phil. Society, 1844. 

f Experiments on Wrought Iron and Steel, pp. 62, 83. 

X Compare Kirkaldy, p. 83, where experiments which are possibly affected 
by the action of vis viva indicate a very similar effect. 



MATERIALS— STRENGTH OF THE STRUCTURE. T) 

scribed, and it may probably be simply another illustration 
of the effect of internal strain. Metals of the " tin class" ex- 
hibit, as has been shown by the Author,^ an opposite effect. 
Rapidly broken, they offer greater resistance than to a static 
or slowly applied load. It has also been seen that annealed 
iron has, in some respects, similar qualities. 

With a very slow distortion the '' flow" already described 
occurs, and but a small amount of internal strain is produced, 
since, by the action noticed when left at rest, this strain re- 
lieves itself as rapidly as produced. A more rapid distortion 
produces internal stress more rapidly than relief can take 
place, and the more quickly it occurs the less thoroughly can it 
be relieved, and the more is the total resistance of the piece 
reduced. Evidence confirmatory of this explanation is found 
in the fact that bodies most homogeneous as to strain exhibit 
these effects least. 

At extremely high velocities the most ductile substances 
exhibit similar behavior when fractured by shock or by a sud- 
denly applied force, to substances which are really compara- 
tively brittle. t In the production of this effect, which has 
been frequently observed in the fracture of iron, although the 
cause has not been recognized, the inertia of the mass attacked 
and the actual depreciation of resisting power just observed, 
conspire to produce results which would seem quite inexpli- 
cable, except for the evidently great concentration of energy 
here referred to, which, in consequence of this conspiring of 
inertia and resistance, brings the total effort upon a compara- 
tively limited portion of the material, producing the short 
fracture, with its granular surfaces, which is the well-known 
characteristic of sudden rupture. Any cause acting to produce 
increased density, as reduction of temperature, evidently must 
intensify this action of suddenly applied stress. 

The liability of machinery and structures to injury by 
shock is thus greatly increased, and it is quite uncertain what 



* Trans. Am. Soc. C. E. , 1874 et seq. 

f Specimens from wrought-iron targets shattered by shock of heavy ora- 
nance exhibit this change in a very unmistakable manner. 



78 THE STEAM-BOILER. 

is the proper factor of safety to adopt in cases in which the 
shocks are very suddenly produced. 

Meantime the precautions to be taken by the engineer are : 
To prevent the occurrence of shock as far as possible, and to 
use in endangered parts light and elastic members, composed 
of the most ductile materials available, giving them such forms 
and combinations as shall distribute the distortion as uniformly 
and as widely as possible. 

The behavior of materials subjected to sudden strain is 
thus seen to be so considerably modified by both internal and 
external conditions which are themselves variable in character, 
that it may still prove quite difficult to obtain mathematical 
expressions for the laws governing them. An approximation, 
of sufficient accuracy for some cases which frequently arise in 
practice, may be obtained for the safety factor by a study and 
comparison of experimental results. 

Egleston, studying the behavior of metal under long-con- 
tinued and repeated stresses, finds evidence of the existence of 
a '' law of fatigue and refreshment of metals," occurring as in- 
dicated by the Author. He also concludes* that metal once 
fatigued may sometimes be restored by rest or by heating 
that '' the change produced is a chemical one," accompanied 
by " a change in the size, color, and surface of the grains of the 
iron or the steel." Surface injuries by blows were found to 
affect the metal, in some cases, to a depth of 15 millimetres 
(0.6 inch). He informs the Author that he finds evidence of 
the formation of crystals in the cold metal during the process 
of becoming fatigued, and a decided change in the proportion 
of combined and uncombined carbon. 

The Effect of Repeated Variation of Load is most important. 
In the year 1859 Pi'of- Wohler, in the employ of the German 
Government, undertook a series of experiments to determine 
the effect of prolonged varying stress on iron and steel. These 
experiments were continued until 1870. The apparatus used 
by Wohler and his successor, Spangenberg, was of four kinds : 

I. To produce rupture by repeated load. 

* Transactions Institute Mining Engineers, 1880. 



MATERIALS— STRENGTH OE THE STRUCTURE. 79 

2. For repeated bending, in one direction, of prismatic 
rods. 

3. For experiments on loaded rods under constant bend- 
ing- stress. 

4. For torsion by repeated stress. 

The amount of the imposed stress was determined by 
breaking several rods of like material, ascertaining the break- 
ing load, and taking some fraction of this for the intermittent 
load. 

From the results of these experiments of Wohler, extend- 
ing over eleven years, the observations here appended were 
deduced : 

" Wohler's Law : Rupture of material may be caused by 
repeated vibrations, none of which attain the absolute breaking 
limit. The differences of the limiting strains are sufficient for 
the rupture of the material^ 

The number A strains required for rupture increases much 
more rapidly than the weight of load diminishes. 

The work of Wohler and Spangenberg has proven what 
was long before supposed to be the fact — that the permanence 
and safety of any iron or steel structure depends not simply 
on the greatest magnitude of the load to be sustained, but on 
the frequency of its application and the range of variation of 
its amount. The structure or the machine must usually be 
designed ta carry indefinitely whatever load it is intended to 
sustain and to be permanently safe, however much the stress 
may vary, or however frequent its application. The stress 
permitted and calculated upon must therefore be less as the 
variation is greater, and as the frequency of its application is 
greater. Although it is customary to make the working load 
one fifth or one sixth the maximum load that could be sus- 
tained without fracture, it has now become well known that 
this is not the correct method except for an unvarying load ; 
although, as will be seen, these factors of. safety are sufficient 
to cover the case studied by Wohler. 

Wohler found that good wrought-iron and steel would bear 
loads indefinitely as follows : 



So THE STEAM-BOILER. 

Lbs. per sq. in. Kilogs. per sq. cm. 

Wrought-iron, tension only + 18,700 to -j- 30; -|- 1,309 to -j- 2.2 

Wrought-iron, tension and compres. + 8,320 to — 8,320; -\- 582 to — 582 

Cast-steel, tension only + 34-307 to + 11,440; -\- 2.401 to -\- 801 

Cast-steel, tension and compression -|- 12,480 to — 12,480; -|- 874 to — 874 

Thus rupture is produced either by a certain load, called 
usually the *' breaking load," once applied, or by a repeatedly 
applied smaller load. The differences of stresses applied, as 
well as their actual amount, determine the number of appli- 
cations which may be made before fracture occurs, and the 
length of life of the member or the structure. This weakening 
of metal by repeated stresses is known as fatigue. It is not 
known that it may always be relieved, like internal stresses, by 
rest ; but it is apparently capable of relief frequently by either 
simple rest for a considerable period, or by heating, working, 
and annealing. 

The experiments described seem to indicate some relation 
between the action of variable loads and of prolonged stress 
where metals are soft enough to '' flow." 

Wohler concluded that the allowable loads for the cases of 
stationary loading, loading in tension alternating with entire 
relief, and equal and alternate tensions and compressions, will 
be in the ratio 3:2: i. 

The method above described is still in the experimental 
stage ; but it may be provisionally accepted as safer than the 
usual method of covering cases of varying stresses by a factor 
of safety determined solely by custom or individual judgment. 
It has been the custom with some American bridge-builders, 
to give members in alternate tension and compression a section 
equal to that calculated for a tension under static load equal 
to the sum of the two stresses — a rough method of meeting 
the most usual and serious case. 

A number of engineers, commenting upon the work of 
Wohler, Spangenberg, Weyrauch, and Launhardt, consider 
that the result is simply to base upon the ultimate strength a 
deduced limit of working stress which corresponds closely to 
the elastic limit, and generally urge that reasonable factors of 



M A l^ERIALS— STRENGTH OF THE STRUCTURE. 8l 

safety related to the limit of elasticity are preferable to the still 
uncertain method above described. It is admitted, however, 
that the results accord with those already indicated by experi- 
ence where a definite practice has become settled upon. 

There are many phenomena which cannot be conveniently 
exhibited by strain-diagrams ; such are the molecular changes 
which occupy long periods of time. These phenomena, which 
consist in alterations of chemical constitution and molecular 
changes of structure, are not less important to the mechanic 
and the engineer than those already described. Requiring 
usually a considerable period of time for their production, they 
rarely attract attention, and it is only when the metal is finally 
inspected, after accidental or intentionally produced fracture, 
that these effects become observable. The first change to be 
referred to is that gradual and imperceptible one which, occu- 
pying months and years, and under the ordinary influence of 
the weather going on slowly but surely, results finally in im- 
portant modification of the proportions of the chemical ele- 
ments present, and in a consequent equally considerable 
change of the mechanical properties of the metal. 

Exposure to the w^eather, while producing oxidation, has 
another important effect : It sometimes produces an actual im- 
provement in the character of the metal. Old tools, which 
have been laid aside or lost for a long time, acquire exceptional 
excellence of quality. Razors which have lost their keenness 
and their temper recover when given time and opportunity to 
recuperate. A spring regains its tension when allowed to rest. 
Farmers leave their scythes exposed to the weather, sometimes 
from one season to another, and find their quality improved by 
it. Boiler-makers frequently search old boilers carefully, when 
reopened for repairs after a long period of service, to find any 
tools that have been lost and so improved. 

36, A Method of Detecting any Overstrain to which a 
structure or either of its parts may have been subjected, which 
was devised, or more properly discovered, by the Author, is 
sometimes of service in revealing danger of accident, or the 
cause of disasters already arrived. It has been shown by the 



82 THE STEAM-BOILER. 

Author^ and by other investigators, that when a metal is sub- 
jected to stress exceeding that required to strain it beyond its 
original apparent, or "primitive," elastic limit, this primitive 
elastic limit becomes elevated, and that strain-diagrams obtained 
autographically, or by carefully plotting the results of well-con- 
ducted tests of such metal, are " the loci of the successive limits 
of elasticity of the metal at the successive positions of set."-f 

It has been shown by the Author also that, at the successive 
positions of set, strain being intermitted, a new elastic limit is, 
on renewing the application of the distorting force, found to 
exist at a point which approximately measures the magnitude 
of the load at the moment of intermission.:}: 

Thus it is seen that a metal, once overstrained, carries per- 
manently unmistakable evidence of the fact, and can be made 
to reveal the amount of such overstrain at any later time with 
a fair degree of accuracy. This evidence cannot be entirely 
destroyed, even by a moderate degree of annealing. Often, 
only annealing from a high heat, or reheating and reworking, 
can remove it absolutely. Thus, too, a boiler, or any structure, 
broken down by causes producing overstrain in its tension 
members, or in its transversely loaded beams (and, probably,, in 
compression members — although the writer is not yet fully as- 
sured of the latter), retains in every piece a register of the 
maximum load to which that piece has ever been subjected ; 
and the strain sheet of the structure, as strained at the instant 
of breaking down, can be thus laid down with a fair degree of 
certainty. The Author has found by subsequent tests that 
transverse strain produces the same effect upon the elastic limit 
for tension. 

Here may be found a means of tracing the overstrains 
which have resulted in the destruction or the injury of any 
iron or steel structure, and of ascertaining the cause and the 
method of its failure, in cases frequently happening in which 

* See Trans. Am. Soc. C. E., 1874 et seq., Journal Franklin Institute, 1874 ; 
Van Nostrand's Eclectic Engineering Magazine, 1874, etc., etc. 

f On the Strength, etc., of Materials of Construction, 1874, Sec. 20. 

:}: On the Mechanical Treatment of Metals; Metallurgical Review, 1877; 
Engineering and Mining Journal, 1877. 



MATERIALS— STRENGTH OF THE STRUCTURE. 



83 



they are indeterminable by any of the usual methods of inves- 



This method may thus sometimes be used to ascertain the 
probable cause of a boiler explosion, by determining whether 
the metal has been subjected to overstrain in consequence of 
overpressure. The causes of accidents to machinery may also 
be thus detected, and many other applications might be sug- 
gested. 

37. The Effect of Temperature and its Variation on iron 
and steel is probably the most important of all those phenom- 
ena which modify the behavior of iron or steel under load. 




752 932 1112 1292 

Fig. 53.— Heat vs. Tenacity. 



800 
14-72 



900 1000 1100 Ci 

1652 1832 F. 



The diagram above* graphically represents the results of 
several series of experiments. 

Curves Nos. i and 2 represent Kollmann's experiments on 
iron, and 3 on Bessemer " steel." No. i is ordinary, and 2 
steely puddled iron. 

Curve No. 4 represents the work of the Franklin Institute 
on wrought-iron. 

* Eisen und Stahl, A, Martens ; Zeitschrift des Vereins Deutscher Inge- 
nieure ; Feb. 18S3, p. 127. 



84 THE STEAM-BOILER. 

Curve No. 5 gives Fairbairn's results, working on English 
wrought-irons. 

Nos. 6 to II are Styffe's, and represent the experiments 
made by him on Swedish iron. The numbers do not appear^ 
as these results do not fall into curves ; these results are indi- 
cated by circles, each group being identified by the peculiar 
filling of the circles, as one set by a line crossing the centre, 
another by one across, a third by a full circle, etc. 

The broken lines, 12 and 13, are British Admiralty experi- 
ments on blacksmiths' irons, and No. 14 on Siemens steel. 

The first five series only are of value as indicating any law ; 
and they exhibit plainly the general tendency already referred 
to, to a decrease of tenacity with increase of temperature. 

Fairbairn's experiments. No. 5, best exhibit the maximum,, 
first noted by the Committee of the Franklin Institute, at a 
temperature between that of boiling water and the red heat. 

It will be observed that the measure of tenacity, at the left, 
is obtained by making the maximum of Kollmann unity. It 
will also be noted that Kollmann does not find a maximumi as 
in curves 4 and 5, but, on the contrary, a more rapid reduction 
in strength at that temperature than beyond. 

It would seem, therefore, that that peculiar phenomenon 
must be due to some accidental quality of the iron.* The 
Author has attributed it to the existence in the iron, before 
test, of internal stresses which were relieved by flow as the 
metal was heated, disappearing at a temperature of 300° or 
400° Fahr. (149° to 204° Cent.). 

The experiments of Mr. Oliver Williams f in determining 
the change produced in the character of the fracture of iron by 
transverse strain, at extreme temperatures, indicate loss of duc- 
tility at low temperatures. 

Two specimens of nut-iron, from different bars, made at 
Catasauqua, Pennsylvania, were first nicked with a cleft on one 
side only, and then broken under a hammer, at a temperature 



* Isherwood suggests that this is simply due to repeatedly breaking the same 
piece. 

f The Iron Age, New York, March 13, 1873, p. 16. 



MATERIALS— STRENGTH OF THE STRUCTURE. 



85 



of about 20° Fahr. (— f Cent.). At this temperature both 
specimens broke off short, showing a clearly defined granular 
or steely iron fracture. The pieces were then gradually heated 
to about 75° Fahr. (24° Cent.), and then broken as before, de- 
veloping a fine, clear, fibrous grain. The two fractures were 




Fig. 54.— Fracture at Okuinakv Temi-ekature. 

but four inches (10.16 centimetres) apart, and are entirely dif- 
ferent. The accompanying illustrations, from the Author's 
collection, exhibit this case. 

It has been long known that a granular fracture may be 
produced by a shock, in iron which appears fibrous when grad- 
ually torn apart. This was fully proven by Kirkaldy.'^ Mr. 
Williams was, probably, the first to make 
the experiment just described, and thus 
to make a direct comparison of the char- 
acteristics of fracture in the same iron at 
different temperatures. 

Valton has found f that some iron be- 
comes brittle at temperatures of 572° or 
752° Fahr. (300° to 400° Cent.), and re- 
gains ductility and toughness at higher 
temperatures. On the whole, the frac- 




FlG. 



55. — Fkactike at Low 
Temperature. 



* Experiments on Iron and Steel. 

f Bulleiin Iron and Steel Assoc, Feb. 1877. 



86 THE STEAM-BOILER. 

ture of iron at low temperatures has been found to be charac- 
teristic of a brittle material, while at higher temperatures it 
exhibits the appearance peculiar to ductile and somewhat vis- 
cous substances. The metal breaks, in the first case, with slight 
permanent set and a short granular fracture, and in the latter 
with, frequently, a considerable set, and the form of fracture in- 
dicating great ductility. The variation in the behavior of iron, 
as it approaches the welding heat, illustrates the latter condi- 
tion in the most complete manner. 

Valton found that a steel rod bent very well at a tempera- 
ture a little below dull red, but broke at a temperature which 
may be called blue, the fracture showing that color. Portions 
of the rod which were below this temperature manifested much 
toughness, and bent without fracture. Charcoal pig-iron from 
Tagilsk, made in 1770, irons obtained from the Ural in rods 
and sheets, soft Bessemer and Martin steels from Terrenoire^ 
soft English steel and good English merchant-bars, all gave 
the same results, whether the metal tested had been hammered 
or rolled. Valton found that the phenomenon had been long 
known to the workmen under his direction. In working sheet- 
iron with the hammer they wait until the metal has cooled 
further when approaching the temperature which would give 
the blue fracture when broken. He concludes that wrought- 
irons, as well as some kinds of soft steel, even when of excel- 
lent quality, are very brittle at a temperature a little below 
dull red heat — 577° to 752° Fahr. (between 300° and 400° Cent.). 

The variation of strength follows quite closely the change 
of density, which latter is illustrated in the preceding diagram^ 
which exhibits increase of volume from the freezing-point. 

The sudden fall of the line before reaching the melting- 
point indicates the sudden increase of volume which castings 
exhibit while cooling, and which enables " sharp" castings to 
be secured. It is at the crest noted near this point that vis- 
cosity is observed. From this point back to the freezing-point 
the variation follows a. regular law. 

It would thus seem that the general effect of increase or 
decrease of temperature is, with solid bodies, to decrease or 
increase their power of resistance to rupture, or to change of 



MATERIALS— STRENGTH OF THE STRUCTURE. 8/ 

form, and their capability of sustaining "dead" loads; and we 
may conclude : 

(i) That the general. effect of change of temperature is to 
produce change of ductility, and consequently change of resili- 
ence, or power of resisting shocks and of carrying '* live loads." 
This change is usually opposite in direction and greater in de- 
gree at ordinary temperatures than the variation simultane- 
ously occurring in tenacity. 

(2) That marked exceptions to this general law have been 
noted, but that it seems invariably the fact that, wherever an 
exception is observed in the influence upon tenacity, an excep- 
tion may also be detected in the effect upon resilience. Causes 
which produce increase of strength seem also to produce a sim- 
ultaneous decrease of ductility, and vice versa. 

(3) That experiments upon copper, so far as they have been 
carried, indicate that (as to tenacity) the general law holds 
good with that metal. 

(4) That iron exhibits marked deviations from the law be- 
tween ordinary temperatures and a point somewhere between 
500° and 600° Fahr. (260° and 316° Cent.), the strength increas- 
ing between these limits to the extent of about 15 per cent 
with good iron. The variation becomes more marked and the 
results more irregular as the metal is more impure. 

(5) That above 600° Fahr. (316° Cent.) and below 70° (21" 
Cent.) the general law holds good for iron, its tenacity increas- 
ing with diminishing temperature below the latter point at the 
rate of from 0.02 to 0.03 per cent for each degree Fahrenheit, 
while its resilience decreases in an undetermined ratio for good 
iron, and to the extent of reduction to one third its ordinary 
value or less, at 10° Fahr. ( — 12° Cent.) when cold-short, and 
in the latter case the set may be less than one fourth that 
noted at a temperature of 84° Fahr. (29° Cent.). 

(6) That the viscosity, ductility, and resilience of metals are 
determined by identical conditions, and that the fracture of 
iron at low temperatures has accordingly been found to be 
characteristic of a brittle material, while at the higher tempera- 
tures it exhibits the appearance peculiar to ductile and some- 
what viscous substances. The metal breaks in the first case 



88 THE STEAM-BOILER. 

with slight permanent set and a short granular fracture, and in 
the latter with frequently a considerable set and a form of frac- 
ture indicating great ductility. The variation in the behavior 
of iron, as it approaches a welding heat, illustrates the latter 
condition in the most complete manner. 

(7) That the precise action of the elements with which iron 
is liable to be contaminated, and the extent to which they 
modify its behavior under varying temperature, remain to be 
fully investigated, but that the presence of phosphorus and of 
other substances producing " cold-shortness," exaggerates to a 
great degree the effects of low temperature in producing loss 
of toughness and resilience. 

(8) That the modifications of the general law with other 
metals than iron and copper, and in the case of alloys, have 
not been studied, and are entirely unknown. 

The practical result of the whole investigation is that iron 
and steel, and probably other metals, do not lose their power 
of sustaining absolutely '' dead " loads at low temperatures, but 
"that they do lose, to a very serious extent, their power of sus- 
taining shocks or of resisting sharp blows, and that the factors 
of safety in structures need not be increased in the former 
case, where exposure to severe cold is apprehended ; but that 
machinery, rails, and other constructions which are to resist 
shocks should have larger factors of safety, and should be most 
carefully protected, if possible, from extreme temperatures. 

The Stress Produced by Change of Temperature is easily cal- 
culated when the modulus of elasticity and the coefificient of 
expansion are known, thus : 

Let E = the modulus of elasticity; 

A = the change of length per degree and per unit of 
length ; 
J/° = the difference of initial and final temperatures; 
/ = the stress produced. 



Then 



p-.Ew X^f : I, 

.-./ = \EAt\ (i) 



MATERIALS— STRENGTH OF THE STRUCTURE. 89 

For good wrought-iron and steel, taking E as 28,000,000 
pounds on the square inch, or 2,000,000 kilogrammes on the 
square centimetre, and A as 0.0000068 for Fahrenheit,, and as 
0.0000120 for Centigrade degrees: 

/ = 190^/° Fahr., nearly, ) 

\ (2) 

= 2^Af Cent., nearly. ) 

For cast-iron, taking E = 16,000,000; A, = 0.0000062: 
p = 100 A f Fahr., nearly, ) 

(3) 

• = 12^/° Cent., nearly. ) 

This force must be allowed for as if a part of the tension, 
T, or compression, C, produced by the working load when the 
parts are not free to expand. 

Sudden Variation of Temperature has an effect upon steel 
which is very great when the proportion of carbon is not far 
from one per cent. With less carbon the effect is less observ- 
able, and with the wrought-irons and with ingot metals con- 
taining less than one third per cent carbon and other hardening 
elements, it becomes quite unimportant. Soft irons are still 
further softened by sudden reduction of temperature from the 
red heat. Cast-irons, unless of the class known as " chilling 
irons," are much less affected than steel, and when very rich in 
graphitic carbon are not perceptibly hardened. 

When either iron or steel is repeatedly heated and cooled, 
a permanent change of form takes place. Colonel Clarke has 
shewn* that cylinders repeatedly heated to a high temperature 
and suddenly cooled, become enlarged in diameter perma- 
nently. Pieces of tempered steel are larger than when untem- 
pered. 

Cast-iron ordnance, after having been discharged many 
times, becomes unsafe in consequence of weakening, which is 



Philosophical Magazine, 1863. 



90 THE STEAM-BOILER. 

probably principally due to strains caused by sudden and irreg- 
ular changes of temperature in service. 

Such grades of steel as take a temper are greatly strength- 
ened unless too highly hardened, in which case they become 
brittle from internal stresses. The Author has found temper- 
ing in mercury to increase greatly both the strength and the 
toughness of small pieces of good tool steel. Kirkaldy has 
found, by an extended series of experiments, that tempering 
tool steels in oil greatly increases both strength and elasticity, 
Avhile hardening in water reduces both. The higher the tem- 
perature at which, without risk, the steel can be cooled, the 
greater is this increase of strength. Hard steels exhibit the 
fact better than soft steels. Dividing steels into series in the 
order of their contents in carbon, beginning with the softest 
grades, the following were the percentages of increase of 
strength from weakest to strongest: 11.8, 24.2, 40.7, 53.2, 57.0,. 
64.1, 70.9, 77.6. The harder steels were highly heated; the 
soft steels only moderately. 

A singular change is observed in iron and in the soft steels,, 
and may perhaps be found to occur with other metals, when 
the temperature approaches what is known as the black heat — ^a 
temperature not far from 600° or 700° F. (316° to 370° C), and 
below a red-heat visible in the dark. At this temperature, 
metal which bends readily either cold or at the full red heat 
is found to be exceedingly brittle and to break easily, especially 
under percussion, without bending. This heat with its peculiar 
effect may be reached in a bath of boiling tallow at a little 
above the lower temperature above specified. The steels show 
less of this effect, usually, than the irons. The presence of 
more than a trace of sulphur, or phosphorus, or of other 
hardening elements, exaggerates this action. 

38. Crystallization and Granulation are the two methods 
of alteration of molecular structure which are consequent upon 
the action of any cause which continually separates the par- 
ticles of the metal beyond the range marked and limited by 
the elastic limit. No evidence is to be found that a single 
suddenly applied force, producing fracture, may cause such a 
systematic and complete rearrangement of molecules. The 



MATERIALS— STRENGTH OF THE STRUCTURE. 9I 

granular fracture produced by sudden breaking, and the crys- 
talline structure produced as above during long periods of time, 
are apparently as distinct in nature as they are in their causes. 
But simple tremor, where no sets of particles are separated so 
far as to exceed the elastic range, and to pass beyond the limit 
of elasticity, does not seem to produce such changes. In fact, 
some of the most striking illustrations of the improvement in 
the quality of wrought-iron with time have occurred where 
severe jarring and tremor were common. Metal has been sub- 
jected for many years to the strains and tremor accompanying 
the passage of trains without apparent tendency to crystalliza- 
tion, and with evident improvement in its quality. 

Wohler found cubic crystals in cast-iron plates which had 
been for some time kept at nearly the temperature of fusion in 
a furnace, and Augustine found similar crystals in gun-barrels ; 
Percy found octahedra of considerable size in a bar which had 
been used in the melting-pot of a glass-furnace. Fairbairn as- 
serts the occasional occurrence of such change due to shock, 
jar, and long-continued vibration. Miller found cubic crystal- 
lization plainly exhibited in Bessemer iron, which may, how- 
ever, have been due to the presence of manganese. Hill 
shows * that heat may produce such crystallization. 

In a discussion which took place many years ago before the 
British Institution of Civil Engineers, Mr. J. E. McConnell 
produced a specimen of an axle which he thought furnished 
nearly incontestable evidence of crystallization. One portion 
of this axle was clearly of fibrous iron, but the other end broke 
off as short as glass. The axle was hammered under a steam 
hammer, then heated again and allowed to cool, after which it 
was found necessary to cut it almost half through and hammer 
it for a long time before it could be broken. The great testing- 
machine at the Washington Navy Yard has a capacity of about 
300 tons, and has been in use 40 years. Commander Beardslee 
subjected it to a stress of 288,000 lbs. (130,000 kilogrammes), 
Avhich stress had frequently been approached before ; but it 
subsequently broke down under about lOO tons. The connect- 

* Iron Age, 1882 , Mechanics, 1882. 



92 



THE STEAM-BOILER. 



ing-bar which gave way had a diameter of five inches, and 
should have originally had a strength of about 400 tons (406,400 
kilogrammes). Examining it after rupture, the fractured sec- 
tion was found to exhibit strata of varying thickness, each 
having a characteristic form of break. Some were quite granu- 
lar in appearance, but the larger proportion were distinctly 
crystalline. Some of these crystals are large and well defined. 
The laminae, or strata, preserve their characteristic peculiarities, 
whether of granulation or of crystallization, lying parallel to 
their axis and extending from the point of original fracture to 
a section about a foot distant, where the bar was broken a 
second time (and purposely) under a steam hammer. It thus 
differs from the granular structure which distinguishes the sur- 
faces of a fracture suddenly produced by a single shock, and 
which is so generally confounded with real crystallizion. 

39. Irons and Steels Compared with reference to their 
composition and qualities, even when the latter are given as 
much of the character of the best iron as is possible, will ex- 
hibit some marked differences. 

In composition the following may be considered good repre- 
sentative examples: 





Irons. 


Steels, 




Swedish. 


Dartmoor. 


Pennsylva- 
nia. 


''Mild." 


Very 
"Mild." 


Carbon 


0.087 
0.056 
0.005 

99.220 


0.016 
0.022 
0. 104 
0. 106 
0.280 
99-372 


0.067 
0.020 
O.OOI 

0.075 

0.009 

99.828 


0.238 
0.105 
0.012 
0.034 
0.184 
99.427 


0.009 
0.163 
0.009 
0.084 
0.620 


Silicon 


Sulphur 


Phosphorus 


Manganese 


Iron by diff 


99-115 






100.000 


100.000 


100.000 


100 . 000 


100.000 



All the hardening elements usually appear in larger propor- 
tion in the steels than in the irons ; but this is not invariably 
the fact, especially with those very mild steels which can be 
made by the crucible process. 

Comparing the analyses of the two classes of metal, it will 
be found that the best irons are more irregular and uncertain 



MATERIALS— STRENGTH OF THE STRUCTURE. 93 

in composition than the best steels; that they contain con- 
siderable amounts of cinder, or slag, derived from the puddle- 
ball and the crude cast-iron from which it is made ; that the 
carbon and silicon are usually less in quantity, though very 
variable; sulphur and phosphorus are commonly *' higher" than 
in steels; and the whole list of elements, aggregating, slag 
aside, less in the irons than in the steels, varies greatly in pro- 
portions, and by no law. The steels are capable of more exact 
prescription of constitution than irons, and are especially dis- 
tinguished by their richness in manganese, silicon, and carbon, 
and their freedom from slag and from sulphur and phosphorus. 
The crucible steels contain, as a rule, much less manganese and 
silicon than do the others. For boiler-plate, the carbon should 
be kept below one fourth of one per cent, and all other ele- 
ments as low as possible ; but the effect of manganese and 
other hardening constituents is not sufficiently well settled, 
especially where the metal is exposed to the action of the fire, 
and to varying temperatures generally, to admit of the pre- 
scription of a formula for the best possible composition. 

Comparing the structure of iron and steel, it will be found 
that the latter is comparatively, often almost absolutely, homo- 
geneous ; while the former is very irregularly laminated, and 
exhibits the most remarkable fibrous texture when broken 
slowly, the slag separating threads of metal by encasing them 
in sheaths of mineral, and layers of cinder and oxide causing 
stratification by preventing the welding of the sheets of thinner 
iron of which the plate is made. The whole structure of the 
*' pile" from which it is rolled is reproduced in a distorted 
fashion in the finished plates. The steel breaks with the same 
fracture, and offers the same resistance in both directions; 
while iron, especially the cheaper grades, usually resists longi- 
tudinal forces much better than transverse. 

In tenacity the best steel boiler-plate is but little, if any, 
stronger than the best boiler-iron : it excels the latter, however, 
in ductility as well as in homogeneousness, and resists the cor- 
roding action of the fluids with which it is brought in contact 
much better than iron. If too rich in manganese, too high in 
carbon or silicon, or if it contains an appreciable amount of 



94 THE STEAM-BOILER. 

phosphorus, steel becomes unreliable, and more dangerous than 
ordinary irons. 

^^ Mild Steer' will take a temper, often, when containing over 
0.30 per cent of carbon. Its uniformity and reliability decrease 
as its strength and hardness increase, and also with increase of 
thickness and size of the mass produced. This fact has caused 
the British Lloyds regulations to make the following allowances : 

Plates and stays o to i inch thick, maximum tensile strength 
67,200 pounds (4724 kgs. per sq. cm.). 

Plates and stays i to if inches thick, maximum tensile 
strength 64,960 pounds (4567 kgs. per sq. cm.). 

Plates and stays over if inches thick, maximum tensile 
strength 62,720 pounds (4410 kgs. per sq. cm.). 

The same proportions carried further would reduce the al- 
lowable tenacity of steel in heavy and thick masses to that of 
good iron, leaving its homogeneousness the only advantage. 

If used at all, the harder steels should be tempered in oil ; 
but they have no place in boiler-construction. 

The conclusions to be to-day reached after comparing steel 
and iron as materials for boiler-construction, and in view of ex- 
perience to date in their use, are fully confirmatory of the as- 
sertion of the late Mr. A. L. Holley, written a generation ago :* 
^' It appears extremely probable that this material " (steel) " will 
gradually come into exclusive service, not only increasing the 
safety and decreasing the repair expense of boilers, but pro- 
moting the economy of steam generation and of railway work- 
ing generally." 

40. The Characteristics of Iron Plate used in boiler- 
making must all be in accordance with the requirements already 
stated. A number of different qualities of both iron and steel 
are sent into the market for use in boiler-construction. Of 
these the makes and qualities of iron have been long well 
settled ; but the best qualities and compositions of steel are 
not as well established. No hard steels, however, are classed 
as boiler-steels. 

Good Boiler-plate is commonly assumed to be made of 

* American and European R ilway Practice, p. 29. 



MATERIALS— STRENGTH OF THE STRUCTURE. 95 

*' charcoal iron," i.e., of iron made from pig-iron produced in 
the charcoal blast-furnace, no other fuel than wood-charcoal 
being used. The scarcity of charcoal and the cost of such irons 
is gradually making it more and more difficult to secure them. 
American boiler-plate is classed by the following-named 
brands : 

^'Charcoal No. i iron" {C. No. i) is made entirely of char- 
coal iron ; it has a tenacity, exceeding 40,000 pounds per square 
inch (2812 kgs. per sq. cm.), is hard, but not very ductile, and 
is never used when flanging or considerable change of form is 
required, as it is apt to break at the bend. When reheated and 
reworked to form what is called " charcoal No. i reheated 
iron" {C. No. i, R. H.) it becomes still harder, and is found to 
wear well in fireboxes, but is still less well fitted than before 
for flanging and working, on account of its increased brittleness. 

" Charcoal Hammered No. i Shell-iron" {C. H. No. i, 5.) is 
a better worked iron than C. No. i ; but it is not always ham- 
mered. It is stronger, having a tenacity of 50,000 to 55,000 
pounds per square inch (3515 kgs. per sq. cm. to 3838) in the 
direction of the fibre, and seventy-five or eighty per cent of 
this amount across the grain. This grade is not usually 
flanged, but may be bent if handled with care, and if the 
radius of curvature is made sufficiently great ; it is sold princi- 
pally for use in the shells of boilers. A better quality known 
as ''flange-iron" {C. H. No. i, F.) is much more ductile, and 
may be worked into flanged sheets ; it is nearly equally strong 
in both directions, and has about the tenacity of the preceding. 
A still harder grade of hammered iron is intended for fireboxes 
mainly (C. H. No. \,F. B.), and especially for flue-sheets, which 
are flanged to receive the flues; and a still better grade {C. H. 
No. ly F. F. B) called "charcoal hammered No. i, flange fire- 
box" iron, extra firebox, or, sometimes, best firebox, is made, 
which is more generally considered best for this use. 

All the grades of charcoal-irons have been made principally 
in Pennsylvania. 

"Shell" boiler-plate has often, if not generally, an outer 
skin of charcoal-iron, the " pile" from which it is rolled being 
composed of other irons, and covered top and bottom with 



9^ TIJE STEAM-BOILER. 

pieces of charcoal-iron. Although distinctively made for the 
shell of the boiler, the best makers usually prefer to use better 
grades for that purpose. 

^'Refined'' Iron is used for miscellaneous purposes when 
strength and toughness are not specially demanded, and where 
no risks are involved. It is not intended for boiler-making; 
it is made directly from the pig-iron. '^ Tank" iron is a still 
cheaper grade, used only for the most unimportant purposes. 
Neither of these grades should be used in boilers, or in any 
structure of great magnitude or value. 

The best British boiler and smith's irons are made in York- 
shire, the best known in the United States being those from 
the Low Moor, the Bowling, and the Farnley works, and sold 
in the trade as " best Yorkshire" irons. 

41. The Manufacture of Boiler-plate, iron or steel, is not 
essentially different in method from the making of other iron 
and steel '' uses." Iron boiler-plate is made from puddled or 
scrap iron, the process of puddling being always that which is 
resorted to in the reduction of the carbon and the production 
of the wrought-iron from the cast. In the rolling of plates, the 
wrought-iron, in bars, slabs, or miscellaneous scrap, is formed 
into '' piles" of the proper size and form, which, after being 
heated to a full welding temperature, are passed through a 
heavy roll-train of sufficient size and power to weld the con- 
stituent pieces into a comparatively solid mass, and to reduce 
that mass to the desired thickness. The pile is made of such 
size and shape as may be found to give the proper form and 
dimensions of sheet. 

Steel plate is oftenest produced by the Siemens-Martin 
process of reduction of cast with wrought iron of selected qual- 
ities, in the " open-hearth" or Siemens regenerative furnace, 
securing freedom from cinder by stirring, and from oxide by 
the addition of manganese in the form either of spiegeleisen 
for hard or of ferro-manganese for soft steels, and then, while 
still very fluid, tapping into the ingot-mould, whence the ingot, 
when sufficiently cooled, is taken to be rolled into plate. An 
intermediate reheating of the ingot, or a period of " soaking" in 
hot "■ soaking-pits," is very generally found advisable to secure 



MATERIALS—STRENGTH OF THE STRUCTURE. 9/ 

a comparative uniformity of temperature throughout the ingot, 
in order that it may be successfully rolled. 

The Bessemer process produces ''steel," or more correctly 
*' ingot-iron," boiler-plate by a very similar series of chemical 
operations; but it usually deals with larger masses, and fur- 
nishes, as a rule, harder steels. The rolling of steel demands 
the use of more powerful roll-trains than are needed in rolling 
iron. 

Comparing the two processes, it is seen that the wrought- 
iron plate must necessarily retain some of the slag which came 
into it from the puddle-ball, and that it must be liable to de- 
fects in welding where the several pieces of which the pile is 
composed come together, especially should those surfaces be 
covered, as is often the case, with a heavy coating of oxide. 
Iron plate must thus always exhibit some defect of homo- 
geneousness, and may be seriously defective in consequence of 
''lamination" produced as just described. On the other hand, 
steel, whether made by the crucible, the Bessemer, or the 
Siemens-Martin process, is always very uniform in texture, and 
is usually so in composition. The molten mass allows all slag 
and oxide to rise to its surface, and thus the fibrous and lami- 
nar character of iron is avoided, while the subsequent processes 
do not involve necessity of welding part to part. It thus hap- 
pens that while iron boiler-plate is a mass of heterogeneous 
constituent elements, and liable to a thousand defects, steel is 
equally remarkable for its unity, homogeneousness, and re- 
liability. 

When an iron surface, parallel to the line of direction of 
rolling of plates, or of drawing down of pieces made or shaped 
under the hammer, is etched, it exhibits plainly the lines of 
" fibre" produced by the drawing out of the cinder originally 
present in the puddle-ball, and reveals any defective weld or 
the presence of any mass of foreign material. When a cross- 
section is made, as in the cases exhibited in the preceding 
figures, the character of the piling is shown, and also that ot 
the workmanship. In these examples, which are reduced to 
one half the size of the originals. Fig. 56 is a section so etched 
of an iron locomotive axle, and Fig. 57 of a steel axle of similar 
7 



98 



THE STEAM-BOILER, 



size and design. The beautiful homogeneousness of good steel 
is exhibited by the almost perfect uniformity of the color and 
texture of the surface ; while the irregularity both of color and 
structure of the other illustration reveals plainly the reasons 
for the variable wearing quality and the inevitable uncertainty 
of strength which must always attend the use of forged iron, 
and especially when made of *' scrap." It is evidently hope- 





FiG. 56.— Locomotive Axle — 
" Special" Iron. 



Fig. 57.— Locomotive Axle — 
Steel. 



less to secure perfect uniformity of structure, texture, and 
strength, or even to obtain soundness, where such great num- 
bers of welds are to be made, and where so much impure and 
foreign material is distributed, hap-hazard, through the mass. 

42. The Methods of Test of iron and steel, relied upon 
to reveal the properties and quality of the metal, are becoming 
well understood and standardized, and are universally practised 
in all important work by experienced and skilful engineers. 

Testing Machines are used for testing small sections and 
pieces of moderate length. They are usually built by manu- 
facturers who make a business of supplying them to engineers 
and other purchasers, and are generally made of several stand- 
ard sizes. The machine is frequently fitted up to test both 
longitudinally and transversely ; although the tests generally 
made are in but one direction. The Author has been accus- 
tomed to keep in use a machine specially intended to test in 



MATERIALS— STRENGTH OF THE STRUCTURE. 



99 



tension and compression, and also separate machines for trans- 
verse and torsional tests. Tension-machine is shown in Fig. 
5'S: it consists of two strong cast-iron columns, secured to a 
massive bed-frame of the same material; above these columns 
is fastened a heavy cross-piece, also of cast-iron, containing two 
sockets, in which rest the knife-edges of a large scale-beam. 
The upper chuck is suspended by eye-rods from knife-edges. 
All the knife-edges are tempered steel, and the sockets and 




Fig. 58. — Tension Testing-machine. 

€yes are lined with the same material, thus reducing friction to 
: minimum. The load is applied by means of a screw, or by 
the hydraulic press, with a fixed plunger and movable cylinder. 
The stress to which the test-piece is subjected is measured by 
means of suspended weights and a sliding poise. The speci- 
men is secured in the chucks either by wedge-jaws or bored 
chucks. 

The extensions are measured by means of an instrument 
(Fig. 59) in which contact is indicated by an " electric contact 
apparatus." This instrument consists of two accurately made 



100 



THE Sl^EAM-BOILER. 




Fig. 59.— Measuring Instrument. 



micrometer screws, working snugly in nuts secured in a frame 
which is fastened to the head of the specimen by a screw 

clamp. It is so shaped that the mi- 
crometer screws run parallel to and 
equidistant from the neck of the spec- 
imen on opposite sides. A similar 
frame is clamped to the lower head of 
the specimen, and from it project two 
insulated metallic points, each opposite 
one of the micrometer screws. Elec- 
tric connection is made between the 
c two insulated points and One pole of a 
voltaic cell, and also between the mi- 
crometer screws and the other pole. 
As soon as one of the micrometer 
screws is brought in contact with the 
opposite insulated point a current is 
established, which fact is immediately 
revealed by the stroke of an electric bell placed in the circuit. 
The pitch of the screws is 0.02 of an inch (0.508 mm.), and their 
heads are divided into 200 equal parts ; hence a rotary advance 
of one division on the screw-head produces a linear advance 
of one ten-thousandth (o.oooi) of an inch (0.00254 mm.). 

A vertical scale, divided into fiftieths of an inch (0.508 mm.), 
is fastened to the frame of the instrument, set very close to 
each screw-head and parallel to the axis of the screw ; these 
serve to mark the starting of the former, and also to indicate 
the number of revolutions made. By means of this double in- 
strument the extensions can be measured with great certainty 
and precision, and irregularities in the structure of the material, 
causing one side of the specimen to stretch more rapidly than 
the other, do not diminish the accuracy of the measurements, 
since half the sum of the extensions indicated by the two screws 
is always the true extension caused by the respective loads. 

The use of the hydraulic press is occasionally found to bring 
with it some disadvantages. The leakage of the press or of the 
pump is itself objectionable, and, where leakage occurs, it i^ 
difficult to retain the stress at a fixed amount during the time 



MATERIALS— STRENGTH OF THE STRUCTURE. lOI 

required in the measurement of extensions. In such cases ab- 
solute rigidity in the machine is important, and the stress should 
be applied by mechanism, which usually consists of a train of 
gearing operated by hand or by power transmitted from some 
prime mover, and itself operating a pulling or compressing 
screw, as in Fig. 56. 

The ''Autographic" Testing-Machine devised by the Author 
is used where it is desired to obtain a knowledge of the general 
character of the metal, including its elasticity and resilience, 
and the method of variation of its normal series of elastic limits, 
and where a permanent graphical record is found useful. It is 
shown in the accompanying figure. 

Fig. 61 is a perspective view of this machine. It consists of 
two A-shaped frames firmly mounted on a heavy bed-plate. 
The frames are secured to each other by cross-bolts. Near 
the top of each of these frames are spindles, each of which 
has a head with a slot or jaw to receive and hold the square 
heads of the specimens. The two spindles are not connected 
to each other in any way, excepting by the specimen which is 
placed in the jaws to be tested. To one spindle a long arm is 
attached, which carries a heavy weight at the lower end. The 
other has a worm-gear wheel attached to its outer end. This 
wheel is driven by a worm on the shaft which is turned by a 
hand crank. When a specimen is placed in the two jaws, and 
the 'spindle is turned by the worm-gear, the effect is to twist 
the specimen which would turn the spindle ; but in order to do 
this the weight on the end of the arm must be swung in the 
direction in which the specimen is twisted. But the farther 
the arm is moved from a vertical position, the greater will b'e 
the resistance of the weight to the turning of the shaft, while 
the movement of the arm and weight is effected by the force 
exerted through the specimen so that the position of the arm 
and weight will at all times give a measure of the torsional 
stress, which is exerted on the specimen by the one spindle, 
and transmitted by the former to the other spindle. 

But as this torsional stress which is exerted on the specimen 
is increased, it will at once commence to " give way," or be 
twisted more or less by the stress according to the quality of 



02 



THE STEAM-BOILER. 



the material. In making such torsional tests, it is essential that 
we should know how much the specimen was twisted, as the 
strains to which it was subjected were increased. If we could 
procure a record of this, it would be an indication of the capac- 
ity of the material to resist such stresses, or, in other words, of 
its quality. The testing-machine which has been described 
was designed by the Author for this purpose. The record is 
made in the following way : To one spindle a cylindrical drum 
is attached, which is covered with a suitable sheet of paper. 
To the pendulum, is attached a pencil, the point of which 
bears on the paper on the drum. Now supposing that the 
specimen in the machine should offer no resistance, but should 
merely twist, the pencil would then remain stationary, and as 
the drum is revolved the pencil would trace a straight line on. 



■^-—Di- 




^ .0 1/' 

Fig. 6o.— Test-piece. 



* 



the paper, the length of which line would measure the amount 
by which the specimen was twisted. If, on the other hand,, 
a specimen be supposed to resist and to twist simultaneously,, 
as is always the case, then it will presently be seen that the 
spindle would be turned, and the arm with the weight would 
be moved from a vertical position a distance proportional to 
the strain resisted by the specimen. The pencil-holder, being 
attached to the arm, would move with it. As explained be- 
fore, the distance which the arm and its weight are moved 
from a vertical position indicates the stress on the specimen. 
Next, in order to make a record of this distance, a " guide- 
curve" is attached to the frame of the machine, so that when 
the pencil-holder is moved out of the vertical position the pen- 
cil is moved toward the left by the guide-curve, which is of 
such a form that the lateral movement which it gives to the 
pencil is proportional to the moment of the weight on the end 



MATERIALS— STRENGTH OF THE STRUCTURE. 



103 



of the arm. Now suppose, if such a thing were possible, that 
a specimen were tested which would not '^ give" or twist at all : 
in that case the spindles, the drum, and the pencil would turn 
together, or their movements would be simultaneous, so that 
the pencil would draw a vertical line along the paper. But 




Fig. 61.— Autographic Machine. 



there is no material known which would not yield or twist 
more or less, so that the pencil will always draw some form of 
curved line, which indicates the quality of the material tested. 
The test-pieces are held in a central position in the jaws by 
lathe '' centres," which are placed in suitable holes drilled in the 



104 THE STEAM-BOILER. 

Spindles for that purpose. The specimen is then held securely 
by wedges. In the diagrams each inch of ordinate denotes lOO 
foot-pounds of moment transmitted through the test-piece, and 
each inch of abscissa indicates lo degrees of torsion. The fric- 
tion of the machine is not recorded, but is determined when the 
machine is standardized, and is added in calculating the results. 

By the use of this machine the metal tested is compelled 
to tell its own story, and to give a permanent record and 
graphical representation of its strength, elasticity, and every 
other quality which is brought into play during its test, and 
thus to exhibit all its characteristic peculiarities. 

The figures on page 105 are derived from a test by tension, 
as made for the Author. On page 106 is given the record of 
a test of steel made by the Ordnance Department, U. S. A. 

43. Tests of Strength and Ductility of irons and steels 
have now been made in such numbers, and with such a variety 
of composition, that the engineer designing or constructing 
boilers need have no doubt in regard to the character of the 
metal to be incorporated in the structure. 

The mean of a considerable number of experiments on ex- 
cellent American iron boiler-plate, made under the eye of the 
Author, gave a tenacity of 54,000 pounds per square inch 
(3795.2 kilogs. per sq. cm.) with a variation of 9 percent; 
flange-iron averaged but 42,000 pounds (2952.6 kgs. per sq. cm.) 
with a variation of nearly 40 per cent ; the highest-priced, 
and presumably best, plate in the market averaged very nearly 
60,000 pounds (4218 kgs.), varying 14 per cent ; and com- 
mon tank-iron showed practically the same tenacity and varia- 
tion as the flange-iron, and less ductility. Thoroughly good 
Pennsylvania plate, in other experiments, gave, for all good 
grades, tenacities not ranging much from 55,000 pounds per 
square inch (3866.5 kilogs. per sq. cm.), and an elastic limit at 
60 per cent of the ultimate strength. Such tenacity is not 
usually to be expected when buying in the market, and it is 
very common, when designing boilers the material of which is 
not prescribed, for the designer to assume that its tenacity may 
not exceed 40,000 pounds (2812 kgs.). On the other hand, a 
contract and specification prescribing careful test may some- 



MATERIALS— STRENGTH OF THE STRUCTURE. 



105 



TEST OF WROUGHT-IRON; LENGTH 8" (19.32 cm.), DIAM. 0.798" (2.03 cm.). 



Loads, 






Extensions. 


Sets. 






Micro 
Reai 


METER 














)INGS. 










Actual. 


Per sq. in. 






\ctual. 


Per cent. 


Actual. 


Per cent. 


150 




.6600 


•7913 










2,000 


4.000 


.6628 


.7910 


.0013 


.016 




.... 


4,000 


8,000 


.6637 


.7922 


0023 


.029 




.... 


6,000 


12,000 


.6646 


.7930 


0035 


.044 


.... 


.... 


8,000 


16,000 


.6606 


.7946 


.0050 


.063 




.... 


10,000 


20,000 


.6630 


.7948 


0058 


.073 






150 


.... 


.6600 


.7914 


.... 




.0001 


.001 


11.000 


22.000 


.6639 


•7951 


0064 


.030 


.... 


... 


12,000 


24,000 


.6700 


.7953 


0070 


•037 






150 




.6603 


•7915 




.... 


.0003 


.004 


13.000 


26,000 


•6715 


.7967 


0080 


.100 


.... 




13,500 


27,000 


.6728 


.7959 


0087 


.109 


.... 


.... 


14,000 


28,000 


.7242 


.8424 


0577 


.721 


.... 


.... 


150 




•7133 


.8351 






.0486 


.608 


15,000 


30,000 


•7535 


.8712 


0867 


1.084 




.... 


150 




•7417 


.8632 


.... 


.... 


.0763 


.960 


17,000 


34.000 


.8474 


.9618 


1790 


2.238 


.... 


.... 


150 




.8326 


.9518 


.... 




.1666 


2.083 


19,000 


38,000 


.9720 


1.0856 


3032 


3.790 


.... 


.... 


150 





.9562 


1.0732 





.... 


.2391 


3-613 


21,000 


42,000 


1. 1710 


I.28II 


5004 


6-255 


.... 


.... 


150 





I. 1524 


1.2663 


.... 


.... 


.4337 


6.043 


22.000 


44,000 


1.3303 


I. 4381 


6586 


8.233 


.... 


.... 


150 




I. 3102 


I. 4212 


.... 




.6401 


8.001 


22,500 


45,000 


1-4575 


1-5441 


7752 


9.690 




.... 


23,000 


46,000 


I. 5610 


1.6670 


8884 


II. 105 


.... 


.... 


23,500 


47,000 


I . 7646 


1.8693 I 


0913 


13.841 


.... 


.... 


23,750 


47.500 


9.. 


M I 


4700 


18.375 


.... 


.... 


21,800 


43,600 


9- 


54 I 


5400 


19.250 


.... 






Lbs. 
1:3,500 



ELASTIC LIMIT. 

Actual. 

Lbs. per 
sq. in. 
6,140 27,000 



Kgs. 



Kgs. per 
sq. cm. 



BREAKING LOAD. 

Original Sect. Fractured Sect. 

Lbs. per Kgs. per Lbs. per Kgs. per 



sq. in. 
47,500 



sq. cm. 
3,340 



69,840 



sq. cm. 
4,910 



Ultimate Elongation, per cent, of 

length = 19;^. 
Reduction of Area, per cent, = 31.99 
Modulus of Elasticity = 24,365,000 

lbs. on sq. in. 
Modulus of Elasticity = 1,712,860 

kilogrammes on sq. cm. 

FINAL DIMENSIONS. 
Length = 9". 54 
Diameter = o".658 



lo6 



Ha: STEAM-BOILER. 



EXTENSION. RESTORATION. AND PERMANENT SET OF A SOLID CYLINDER 
OF STEEL, 3 INCHED LONG (BE I'WEEN SHOULDERS) AND 0.622 INCH 
DIAMETER. TAKEN FROM BREECH-RECEIVER FOR ii-INCH BREECH- 
LOADING RIFLE. 



* Specimen broke. 



Weight 


Extension 
per inch 
in Length. 


Successive 


Restoration 

per inch 
in Length. 


Successive 


Permanent 


Successive 


per e quare 


Extension 


Restoration 


Set 


Permanent 


inch of 
Section. 


per inch 
in Length. 


per inch 
in Length. 


per inch 
in Length. 


Set per inch 
in Length. 


Pounds. 


Inches. 


Inches. 


Inches. 


Inches. 


Inches. 


Inches. 


1,000 


. 00000 


0.00000 


. 00000 


0.00000 


0.00000 


0.00000 


2,000 


.00000 


.00000 


. 00000 


. 00000 


. 00000 


.00000 


3,000 


.00000 


. 00000 


. 00000 


.00000 


. 00000 


.00000 


4,000 


.00033 


■00033 


.00033 


.00033 


.00000 


.00000 


5.000 


.00033 


.00000 


.00033 


. 00000 


. 00000 


.00000 


6.000 


.00033 


.00000 


.00033 


.00000 


. 00000 


.00000 


7,000 


.00033 


.00000 


.00033 


. 00000 


.00000 


.00000 


8,000 


.00033 


.00000 


.00033 


. 00000 


.00000 


.00000 


9,000 


.00033 


. 00000 


.00033 


.00000 


. 00000 


.ooooo- 


10,000 


.00033 


.00000 


.00033 


.00000 


.00000 


.00000 


11,000 


.00033 


.00000 


.00033 


. 00000 


.00000 


.ooooo- 


12,000 


.00033 


.00000 


•00033 


.00000 


.00000 


.00000 


13,000 


.00033 


.00000 


.00033 


.00000 


. 00000 


. ooooo- 


14,000 


.00033 


. 00000 


.00033 


. 00000 


.00000 


. ooooo 


15,000 


.00033 


.00000 


.00033 


. 00000 


. 00000 


.00000- 


16,000 


.00067 


.00034 


.00067 


.00034 


.00000 


. ooooo 


17,000 


.00067 


. 00000 


.00067 


. 00000 


.00000 


.00000 


18,000 


.00067 


.00000 


.00067 


. 00000 


.00000 


. ooooo- 


19,000 


.00133 


.00066 


.OOIOO 


•00033 


•00033 


•00033 


20,000 


.00233 


.00100 


.00100 


.00000 


.00133 


.OOlOO- 


21,000 


.00300 


.00067 


.00100 


. 00000 


.00200 


. 00067 


22,000 


.00400 


. 00100 


.00100 


.00000 


.00300 


.OOIOO- 


23,000 


.00467 


.00067 


. 00 1 00 


. 00000 


.00365 


.00067 


24,000 


.00533 


.00066 


.00100 


.00000 


.00433 


.00066 


25.000 


.00633 


.00100 


•00133 


.00033 


.00500 


.00067 


26.000 


.00700 


. 00067 


•00133 


.00000 


.00567 


.00067 


27.000 


.00767 


. 00067 


.00133 


. 00000 


.00633 


.00066 


28,000 


.00900 


•00133 


.00100 


— .00033 


.00800 


.00167 


29,000 


.00967 


.00067 


.00100 


.00000 


.00867 


.00067 


30,000 


.01067 


.00100 


.00133 


•00033 


.00933 


.00066 


31,000 


.01200 


.00133 


■00133 


.00000 


.01067 


.00134 


32,000 


.01300 


■ .00100 


.00167 


.oooH 


.01133 


.00066 


33.000 


•01433 


.00133 


.00167 


. 00000 


.01267 


•00134. 


34.000 


.01567 


•00134 


.00133 


— .00034 


•01433 


.00166 


35,000 


.01700 


•00133 


.00133 


.00000 


.01567 


•00134 


36,010 


.01800 


.00100 


.00133 


.00000 


.01667 


.OOIOO- 


37,000 


.01967 


.00167 


.00133 


.00000 


.01833 


00166 


38,000 


.02133 


.00166 


.00167 


.00034 


.01967 


.00134 


39,000 


.02433 


. 00300 


.00167 


. 00000 


.02267 


.00300- 


40,000 


.02567 


•00134 


.00167 


. 00000 


.02400 


•00133 


41,000 


.02733 


.00166 


.00167 


.00000 


.02567 


.00167 


42,000 


.02867 


.00134 


.00167 


. 00000 


.02700 


.00 J 33. 


43,000 


•03033 


.00166 


.00200 


•00033 


.02833 


.00133 


44.000 


.03300 


.00267 


.00233 


.00033 


•03067 


.00234 


45,000 


•03433 


•00133 


.00200 


— .00033 


.03233 


.00166- 


46,000 


.03900 


.00467 


.00233 


.00033 


.03667 


.00434 


47,000 


.04167 


.00267 


.02223 


.00000 


•03933 


.00266 


48,000 


.04367 


.00200 


.00233 


.00000 


•04133 


. 00200 


49,000 


.04700 


.00333 


.00267 


.00034 


•04433 


. 00300- 


50,000 


.05100 


.00400 


.00200 


— .00067 


.04900 


.00467 


51,000 


•05533 


.00433 


.00300 


.00100 


•05233 


•00333. 


52,000 


.06067 


•00534 


.00233 


— .00067 


•05833 


. 00600 


53,000 


.06667 


.00600 


. 00300 


.00067 


.06-.67 


•00534 


54.000 


.06897 


.00200 


•00233 


— .00067 


•06633 


.00266- 


55.000 


.07867 


.01000 


. 00300 


.00067 


•07567 


•00934 


56,000 


•08333 


.00466 


.00300 


.00c 00 


.08033 


. 00466- 


57.000 


.09500 


.01167 


. 00300 


.00000 


.0Q200 


.01167 


58,000 


.10233 


•00733 


.00333 


.00033 


.09900 


.00700- 


59,000 


.11800 


.01567 


.00333 


.00000 


.11467 


.01567 


60,000 


.13700 


.01900 


.00367 


•00034 


•13333 


.01866 


61,000 


.16900 


.03200 


0.00400 


0.00033 


0. 16^00 


0.03167 

(*) 


62.000 


0.30367 


0.13467 


(*) 


(*) 


(*) 



GENERAL 

Tensile Strength per sq. in lbs. 62.000 

Elastic limit lbs. 19.000 

Extension per in. at elastic limit in. 0.00133 

Extension per in. at rupture in. 0.30367 



SUMMARY. 
Original area of cross-section. . 

Area after rupture 

Position of rupture .\^ 

Character of fracture 



. sq. in. 0.3038- 
.sq. in. 0.1611 
from shoulder. 
Fibrous» 



III 



MATERIALS— STRENGTl'J OF THE STRUCTURE. 10/ 

times secure iron, if thin, capable of sustaining 60,000 pounds per 
square inch (4218 kilogs. per sq. cm.). A fair contract figure, and 
one that may be assumed in designing when the iron is to be 
thus selected and tested, would be considered to be 55,000 
pounds (3867 kilogs.). 

Steel boiler-plate of high tenacity is so certain to involve in 
its use risk of cracking, either in the process of construction, or 
later, after exposure to variations of temperature, and to alter 
so seriously and so uncertainly in all its physical properties, 
that specifications usually prescribe that it shall not exceed 
60,000 pounds (4218 kilogs.) tenacity, and in some cases the 
figure is put even lower. When first introduced, tenacities 
much greater were allowed for steels, and great risks, and often 
serious accidents and losses of life and property, were the conse- 
quence. All good boiler-irons should be expected to stretch at 
least 20 per cent of the length of the test-piece, the latter being 
made at least four or five, and better eight or ten, diameters, 
or breadths in length. The best irons stretch 25 per cent, and 
the best steels even more. Thick plates have less tenacity and 
less ductility than thin. 

The " bending test " is one which only the best of irons and 
the softer steels will bear. The strip cut from the sheet for 
test, the " coupon" as it is called, if of less than f inch thick- 
ness, should bend completely over and be hammered flat upon 
itseU", as in the figure. 




Fig. 62. — Bending Test. 

Steels subjected to the " temper test," by heating the sam- 
ple red-hot and quenching in cold water, should then, if of 
good quality for boilers, be capable of successfully passing the 
bending test ; but it is not usually demanded that it shall close 
down flat. If it bends to a circle of a diameter less than three 
times its own thickness, it is accepted. Steels subjected to the 
*' drifting test " are commonly drilled with a -f-inch drill, and 
the hole drifted out as large as possible. If it is enlarged to 



I08 THE STEAM-BOILER. 

double its original diameter, the metal is usually accepted; 
but it is sometimes demanded that it shall bear extension to 
two inches in diameter, as for example at Crewe, on the Lon- 
don and Northwestern Railway of Great Britain. 

44. Specifications of Quality, as well as of kind and form, 
of materials proposed to be used in steam-boiler construction 
are so drawn as to secure not only an understanding on the part 
of the maker or vender of the exact nature of the intended 
provisions, but also a means of certainly determining whether 
those specifications and the contract are fully complied with. 

Wrought-iron and steel, as has been seen, are very variable 
in strength and other qualities. For small iron parts, a tenacity 
of 55,000 to 60,000 pounds per square inch (3867 to 4218 kilo- 
grammes per square centimetre) is usually called for ; but the 
strength of plate or of large masses is rarely three fourths as 
great. The specification usually calls for '' iron of the best 
quality," tough, of a definite tenacity, fibrous, free from cinder- 
streaks, flaws, lamination or cracks, uniform in quality, and 
with a prescribed elastic limit, and often a stated modulus of 
elasticity. Even the method of piling, heating, and rolling or 
hammering is specified. 

As has been shown fully in the preceding chapters, the di- 
mensions must be determined after a careful consideration of 
the character and the method of application of the load, as 
well as of its magnitude, and allowance must be made by the 
engineer for the effect of heat or cold, of repeated heating in 
the process of manufacture, for the rate of set under load, for 
the rapidity of its application, or for the effect of repeated or 
reversed strains. 

The differences in the behavior of the several kinds of iron 
or steel under the given directions must be considered in pro- 
portioning parts. Thus unannealed iron or 'Mow" steel will be 
chosen for parts exposed to steady and heavy loads ; the use of 
annealed metal will be restricted to cases in which the primary 
requisite is softness or malleability ; steel containing about 0.8 
per cent carbon will be given the preference for parts exposed 
to moderate blows and shocks which are not expected to ex- 
ceed the elastic resilience of the piece ; tough, ductile metal, 



MATERIALS— STRENGTH OF THE STRUCTURE, IO9 

preferably "ingot iron," will be chosen for parts exposed to 
shocks capable of producing great local or general distortion. 

" Wuhler's Law" dictates the adoption of increased factors 
of safety, or of some equivalent device, as Launhardt's formula, 
when variable loads are carried. Thus the engineer is com- 
pelled to make a specification, in very important work, which 
shall prescribe all the qualities of materials and exactly the 
proportions of parts needed to make his work safe for an in- 
definite period. 

Steel has such a wide range of quality that few difficulties 
are met with in its introduction into any department of con- 
struction. In boiler-work, however, it must be kept low in car- 
bon, and therefore in tenacity ; and in machinery and bridge 
work, also, its composition must be carefully determined upon, 
and as exactly specified. 

The following are good specifications for boiler-work: 

Steel Sheets. — Grain — To be uniform throughout, of a fine 
close texture. Workmanship — Sheets to be of uniform thick- 
ness, smooth finish, and sheared closely to size ordered. Tensile 
Strength — To be 60,000 pounds to square inch for firebox 
sheets, and 55,000 pounds for shell sheets. Working Test — A 
piece from each sheet to be heated to a dark cherry red, plung- 
ed into water at 60°, and bent double, cold, under the hammer ; 
such piece to show no flaw after doubling. 

Iron Sheets. — Grain — To be uniform throughout, showing 
a homogeneous metal with no layers or seams. Workmanship 
— Sheets to be of uniform thickness, smooth finish, and sheared 
closely to size ordered. Tensile Strength — To be 60,000 pounds 
to the square inch for firebox sheets, and 55,000 pounds for 
shell sheets. Working Test — A piece from each sheet to be 
bent cold to a right angle, showing no fracture. A piece bent 
double, hot, to show no flaking or fracture. 

Specifications for Boiler Tubes. — Size — Locomotive tubes 
to be 12 feet long and 2 inches diameter; to be of iron. No. 
1 1 gauge. Quality of Metal — When flattened under the ham- 
mer to show tough fibrous grain ; when polished and etched 
with acid to show uniform metal and a close weld. Workitig 
Tests — When expanded and beaded into the flue-sheet to show 



no THE STEAM-BOILER. 

no flaws ; to stand '^ swaging down " hot without flakes or 

seams. 

The following are specifications for Boiler and Firebox Steel : 
(i) A careful examination will be made of every sheet, and 

none will be received that show mechanical defects. 

(2) A test strip from each sheet, tested lengthwise. 

(3) Plate will not be passed for acceptance when of 
strength of less than 50,000 or greater than 65,000 pounds per 
square inch, nor if the elongation falls below twenty-five per 
cent. 

(4) Should any sheets develop defects in working they will 
be rejected. 

(5) Manufacturers must send one test strip for each sheet 
(this strip must accompany the sheet in every case), both sheet 
and strip being properly stamped with the marks designated 
by the company, and also lettered with white lead, to facilitate 
marking. 

The U. S. Board of Supervising Inspectors of Steam-vessels 
restrict the stress on boiler stays and braces to 6000 pounds 
per square inch (4218 kilogrammes per square centimetre). For 
shells of boilers, a factor of safety of 6 is permitted in design- 
ing. The hydrostatic pressure applied in testing is one half 
greater than the steam-pressure allowed. All plates must be 
stamped by the maker with the tenacity, as determined by test, 
at the four corners and in the middle. The elongation is not 
noted, as the form of United States standard test-piece is 
unfitted to determine it. The contraction of area of section at 
fracture must be 0.15 when the tenacity is 45,000 pounds and 
one per cent more for each additional 1000 pounds. 

Hot-short, or red-short, and cold-short irons are detected by 
the forge tests ; the former is often found to be an excellent 
quality of iron if it can be worked into shape, as it is, when cold, 
tough and strong. Specially high qualities are rarely economi- 
cal, as they usually cost too much to make the difference worth 
what is paid for it. Shapes difficult to make or roll are usually 
weaker than others. Mills will usually supply '' pattern iron," 
charging a little extra for it ; but it will often be found economi- 
cal to order them, if such shapes are necessary. In designing, 



MATERIALS— STRENGTH OF THE STRUCTURE. Ill 

however, it is well to avoid the introduction of peculiar shapes, 
if possible. 

All wrought-iron, if cut into testing strips one and a half 
inches in width, should be capable of resisting without signs of 
fracture, bending cold by blows of a hammer, until the ends of 
the strip form a right angle with each other, the inner radius of 
the curve of bending being not more than twice the thickness of 
the piece tested. The hammering should be only on the ex- 
tremities of the specimens, and never where the flexion is tak- 
ing place. The bending should stop when the first crack ap- 
pears. 

All tension tests should be made on a standard test-piece of 
one and a half inches in width, and from one quarter to three 
<quarters of an inch in thickness, planed down on both edges 
equally so as to reduce the width to one inch for a length of 
eight inches. Whenever practicable, the two flat sides of the 
piece should be left as they come from the rolls. In all other 
cases both sides of the test-piece are planed off. In making 
tests the stresses should be applied regularly, at the rate of 
about one ton per square inch in fifteen seconds of time. 

All plates, angles, etc., which are to be bent in the manu- 
facture should, in addition to the above requirements, be 
capable of bending sharply to a right angle at a working test, 
without showing any signs of fracture. 

All rivet-iron should be tough and soft, and pieces of the 
full diameter of the rivet should be capable of bending until 
the sides are in close contact, without showing fracture. 

All workmanship should be first-class; all abutting surfaces 
planed or turned, so as to insure even bearing, taking light cuts 
so as not to injure the end fibres of the piece, and protected by 
white lead and tallow. Pieces where abutting should be brought 
into close and forcible contact by the use of clamps or other 
approved means before being riveted together. Rivet-holes 
should be carefully spaced and punched, and in all cases reamed 
to fit, where they do not come truly and accurately opposite, 
without the aid of drift-pins. Rivets should completely fill the 
lioles, and have full heads, and be countersunk when so required. 

The following are specifications originally issued by the 





Tenacity. 




Lbs. per sq. in. 
60,000 
70,000 
80,000 
90,000 






Kilos, per sq. cm. 
4218 
4921 
5624 
6327 



112 THE STEAM-BOILER, 

United States Navy Department, which indicate the relation 
of variation of tenacity to the corresponding change in ductil- 
ity where the quantity of carbon in steel is altered : 



Extension. 
Per cent. 

25 

23 

19 
12 



A cold-bending test is demanded thus: Bend the strip over 
a mandrel of a diameter ij times the thickness of the plate, 
through an arc of 90°, and no cracks must appear with the 
softer grades, and any cracks seen in the case of the harder 
steels must be insignificant. 

Every reputable maker stamps his iron, not only with the 
figures indicating the tenacity, as required by law, but also, in 
the case of thoroughly good qualities, with their names. Where 
the brand is not found, it is assumed by the experienced en- 
gineer that the metal is not of such high quality as to do credit 
to the maker. All good plate is expected to have fair tenacity 
and high ductility, and good flange-iron should not deteriorate 
appreciably in working. 

45. Choice of Quality of Metal for the Various Parts 
of a boiler or other structure is made with the greatest care by 
the designer and by the constructor. The furnace, exposed as 
it is to variations of temperature, to the corrosive effect of hot 
gases, and to the mechanical wearing action of the cinder and 
coal carried by their rapidly moving currents, is made of the 
harder qualities of iron or steel already described. The tubes, 
flues, and the flue-sheets are composed of comparatively ductile 
material, such as may be safely shaped in accordance with the 
plans of the designer ; the shell may be of cheaper material ; 
while all stays and braces must be made of the strongest and 
toughest metal available. Each grade should be carefully pre- 
scribed, and the iron or steel proposed for use as carefully in- 
spected and tested before it is introduced into the structure. 
It is sometimes advisable to substitute copper for iron, espe- 



MATERIALS— STRENGTH OF THE STRUCTURE. II3 

cially in the firebox; and in such cases sheet-copper of a tena- 
cious and somewhat hard quaUty should be adopted. This ma- 
terial usually has about two thirds the strength of good iron, 
with greater ductility and flexibility, and resists the action of 
the furnace gases better than iron boiler-plate. 

46. The Methods of Working the materials introduced 
into steam-boilers are adapted very carefully, in every case, to 
the known requirements of each quality so used. The frequent 
injury of steel and of hard iron plates by punching and by too 
abrupt change of form have led engineers to prescribe in 
many cases that all steel plate shall be drilled for the insertion 
of rivets, and not punched, and to direct the bending of the 
plate over rounded edges having comparatively large radii of 
curvature. All wrought-iron work in boilers, when subjected 
to any considerable change of form, should be worked at a 
bright-red heat, approaching the welding temperature ; steel 
should be handled, in such cases, at a *' cherry-red " heat. 

Great alteration of shape, if effected at ordinary tempera- 
tures, should be made slowly and carefully, and it may even be 
well in some instances to allow intermissions in such opera- 
tions sufficient to permit the particles some opportunity of 
self-adjustment. It may be taken as a general rule in the work- 
ing of all materials for steam-boilers, that the methods and pro- 
cesses chosen should always be such as will be least likely to 
strain or to injure, either generally or locally, the iron or steel 
so used. 

47. Special Precautions in Using Steel are found to be 
necessary to secure safe construction. Construction in steel 
demands more care than the making of iron boilers, and a good 
boiler-maker for the latter class of work is not necessarily a 
good worker of steel. In handling steel for boilers there should 
be no unnecessary local heating. If so heated, steel should 
always be subsequently annealed. The plates for the cylindri- 
cal shells of boilers should be carefully bent to shape when 
cold. The rivet-holes should usually be drilled, not punched, 
and the drilling should be done after the plates are bent to 
shape, and bolted together in position. The longitudinal 
joints in the shell are best made with double butt-strips, one 



H4 THE STEAM-BOILER. 

being placed inside, and the other outside, to form a " butt 
joint." 

The tests of the plate supplied on specifications, and under 
contracts, should be even more carefully and minutely made 
than with iron ; every operation must be more carefully con- 
ducted and supervised, and the completed boiler should be 
inspected and tested with the greatest possible care. If it is 
well made and of good material, it will be a more satisfactory 
construction than any iron boiler can possibly be ; a mistake in 
accepting and using steel ill adapted to the purpose may 
produce an exceedingly dangerous and unsatisfactory boiler. 
Steel of good quality, and well adapted for other construction, 
is not necessarily safe for use in steam-boilers. 

Many engineers would anneal every plate of steel used, 
whatever its apparent quality, to insure its safety in the struc- 
ture, and it has even been suggested that it would be well, were 
it practicable, to anneal the whole boiler after completion."^ 
Too great care cannot be taken in selecting the metal. 

48. Rivets and Rivet-Iron and Steel are necessarily of 
especially good quality. The rivet must be strong, tough, and 
ductile, and capable of bearing the severest deformation at all 
temperatures without injury. It is customary to '^ head-up" 
rivets hot ; but medium-sized and small rivets, in some locali- 
ties, are worked cold, and this is the most trying test of quality 
possible. Rivets of less than f-inch (0.95 cm.) diameter are 
very commonly driven cold. Rivet-iron should, in the bar, 
have a tenacity approaching 60,000 pounds per square inch 
(4218 kgs. per sq. cm.), and should be as ductile as the very 
best boiler-plate when cold. The rivet should be capable of 
bearing the change of form incidental to its use without ex- 
hibiting a tendency to split; the head should not seriously 
harden or become brittle under the blows of the hammer ; and 
the contraction on cooling, after it has been headed up, should 
not cause weakening by the stress incident to the strain so 
produced. A good iron rivet f inch (1.6 cm.) diameter can be 
doubled up and hammered together, cold, without exhibiting 

* Trans. Am. Soc. M. E., 1887, No. ccxlvi. 



MATERIALS— STRENGTH OF THE STRUCTURE. II5 

a trace of fracture. Such a rivet, split and "etched" on the 
cut surfaces, shows a smoothly curved grain, uniform texture 
and color, and no visible sign of the presence of slag. Such a 
rive.t, made of good rivet-steel, will show absolute uniformity 
of surface, and no trace even of '* grain." 

The chemical composition of these rivet-steels should be as 
nearly as possible that of the best rivet-irons ; they should con- 
tain the least possible proportion of the hardening elements, 
including carbon and manganese, as well as phosphorus, and 
should be so pure as to readily take a surface like that of a 
mirror, when polished. 

49. The Sizes of Rivets, their form and strength, are 
quite well settled by experience and by test. The rivet con- 
sists, as supplied by the market, of a straight or slightly tapered 
body, circular in section, and having a head 1.5 or 1.6 the di- 
ameter of the shank; the latter is 2 to 3 or 4 per cent smaller 
than the hole which it is to fill, and tapers toward the end to 
a diameter about 0.95 that of the hole. The head is cylindri- 
cal, and has a thickness 0.7 or 0.75 the diameter of the body of 
the rivet. The length of the shank or body is 2.25 or 2.50 
times the diameter of the hole, and the latter is often equal to 
the double thickness of plates held together by it. When in 
place, the small end is driven down by hand-hammers or by the 
riveting machines to form a cone-shaped or hemispherical 
head, the sheets riveted together being thus confined by the 
two heads and sustained by the strength of the shank against 
any force tending to separate them. The principal stresses 
exerted on the rivet are usually shearing. The rivets, when 
heated, should be brought up to a full, clear red heat. A 
simple rule sometimes used to determine the diameter of a 
rivets is that of Unwin, who makes this diameter 



d= 1.2 1//, 

in which t is the thickness of the single plate or sheet. The 
following table is thus obtained, taking the nearest yV^^ • 



ii6 



THE STEAM-BOILER. 



Thickness 
of Plate. 



Diameter, d, 
of Rivet. 

i =0.50 
x'e = 0-56 
\\ = 0.68 

f = 0.75 

H = 0.80 



Diameter, d, 
of Rivet. 



Thickness 
of Plate. 

i\ i =0.86 

t tI = 0-94 

f ItV= i-o6 

i •■" li = I-I3 

I ij = 1-25 



The driven rivet is something like four or five per cent 
larger than the undriven. 

The following table gives the proportions of rivets adopted 
in some of the best establishments in the United States,"^ and 
the relative strength of joint secured: 

TABLE OF THE PROPORTIONS OF RIVETS. 



Thickness of plate 

Diameter of rivet 

Diameter o rivet-hole 

Pitch — single-riveting 

Pitch — double-riveting 

Strength of single-riveted joint. 
Strength of double-riveted joint 



X" 


A" 


f" 


tV 


i 


11 


i 


13 


16 


4 


16 


H 


f 


it 


i 


2 


%v 


2i 


2^ 


3 


3i 


3i 


3f 


.66 


.64 


.62 


.60 


.77 


.76 


.75 


•74 



T6 

2i 

3i 

,58 

.73 



Plates more than |-'' thick should never be joined with lap- 
joints. When it is necessary to use them a butt-joint with a 
double fish-plate should always be used. In recommending the 
above proportions we assume that the workmanship is always 
fair. 

The common proportions of rivets, as given by Unwin,f are 
seen in the accompanying figure ; that 
illustrated is of such form as will permit 
the formation of the conical head, the 
total length being about 2^ times the 
diameter when a double thickness of 
plates is to be secured together. 

The next figures exhibit the differ- 
ence in proportions of rivets for hand- 
riveting and for steam-riveting, as given 
Fig. 63. by the same authority; the first figure 

showing two forms of head for hand-work, the second two for 

* Locoinoti%L\ July, 1882. 
\ Machine Design. 




MATERIALS— STRENGTH OF THE STRUCTURE. 1 17 
Steam-riveted work : one of each pair is set in a straight hole, 




-14S 




Fig. 64. 



Fig. 65. 



)4-'$J-^. 



the other in a chamfered hole. The next figure gives the pro- 
portions for a countersunk rivet, used in ship-building. 

50. The Strength of Seams, when riveting is used, varies 
with the character of the metal, the method of riveting, and 
the quality of workmanship. A single-riveted joint has usually 
not far from 60 per cent of the strength of the solid sheet, a 
double-riveted seam 70 per cent ; and 
the strength may be still further in- 
creased by adding to the number of 
rows of rivets, with proper distribu- 
tion. The joint is so proportioned 
that the fracture will occur by shear- 
ing the rivets rather than by breaking 
out the edge of the sheet or tearing 
away the lap bodily. The lap usually 
extends beyond the rivet-hole about 
1.5 times the diameter of the rivet. 

To secure maximum '* efificiency" of seam, i.e., equal and 
maximum resistance in all directions of possible stress, it is 
evident that the joint must be equally liable to tear along the 
line of rivets, to shear the rivets, and to tear them out by pull- 
ing them through the lap. For a single-riveted joint there- 
fore, if F represent the tearing force, T the tenacity of the 
sheet, SS' the shearing resistance of the rivet and sheet, Cits 
resistance to crushing,/ the '' pitch," and </ the diameter of the 




Il8 THE STEAM-BOILER. 

rivets, / the width of lap, and t the thickness of the sheet, we 
must have 

F=\nd''S' = Cdt = {p- d)Tt = \{2l - dyXt; 

or, if the lap is made over strong, as above, and if crushing is 
not anticipated, both of which are usual conditions, 



and 



F=^7td"S ^{p-d)Tt, 



^Ttd'S+dtT I Ttd'S ^ 



•Where, as sometimes is the case, the joint is a butt-joint 
and the rivets are thus " in double shear," 

^nd'S + d 
^ = Tf—'^ 

and the same expression serves for the case of double-riveted 
seams made, as with single-riveting, with a lap, but having a 
second line of rivets behind and reinforcing the first. 

Where the rivet and the plate are of the same material, or 
wherever the resistance to shearing and the tenacity may be 
taken as substantially equal, the formula 

p^d-\ 7 ■ 



may be adopted, in which /, d, n, and t are, respectively, the 
pitch of rivets, centre to centre, the diameter of rivet, the 
number of parallel rows, and the thickness of sheet. 

The following tables represent proportions for adoption in 
designing, the ratio of 7" to 6" being taken for iron and steel of 
various qualities, as assumed by Unwin :* 



* See Machine Design, by W. C. Unwin. London : Longmans, Green & Co. 



MATERIALS— STRENGTH OF THE STRUCTURE. 



119 



SINGLE-RIVETING. 





^IN Inches. 


Ikon Rivets 


AND Plates. 


Steel Rivets 


AND Plates. ■ 




Punched 


Plates 


Plates 


Plates Drilled 


i 






Plates. 


Drilled. 


Punched. 


and Annealed. 




Nomi- 
nal. 


Actual. 




Pit( 


:h / for ^ 


/alues of 


T _ 

C ~ 












0.75 


0.85 


0.95 


I.O 


1.05 


1. 15 


1.25 


1-35 


h 


H 


0.72 


2.45 


2.25 


2.1 


2.0 


2.0 


1.85 


1.8 


1-7 


1 


f 


0.78 


2.5 


2.3 


2.1 


2.1 


2.0 


1.9 


1.8 


T-7 


tV 


H 


0.85 


2.6 


2.4 


2.2 


2.15 


2. I 


2.0 


1.9 


1.8 


i 


i^ 


0.92 


2.7 


2.5 


2.3 


2.2 


2. I 


2.1 


2.0 


1.9 


4 


1^ 


0.q8 


2.6 


2.4 


2.3 


2.2 


2.1 


2.0 


2.0 


1.9 


4 


ItV 


1, 10 


2.8 


2.6 


2.4 


2.4 


2-3 


2.2 


2.1 


2.0 


i 


li 


1. 17 


2.9 


2.7 


2.5 


2.5 


2.4 


2.25 


2.2 


2.15 


I 


li 


1.30 


3-1 


2.9 


2.7 


2.6 


2.6 


2.45 


2.4 


2.3 



DOUBLE-RIVETING. 









Iron R 


ivETs.— Plates 


Steel Rivets.— Plates 




^ IN Inches. 










t 






Punched. 


Drilled. 


Punched. 


Drilled. 








Pitch of rivets 


T 
for value of — = 






Nomi- 


Actual. 






C 






nal. 




















0.85 


1. 00 


1. 10 


1.20 


1-35 


h 


H 


0.72 


3.8 


3-3 


3-1 


2.9 


2.7 


1 


\ 


0.78 


3.8 


3 


4 


3 


I 


2 


9 


2.7 


l^r 


\l 


0.85 


3-9 


3 


5 


3 


2 


3 





2.8 


i 


¥ 


0.92 


4.0 


3 


6 


3 


4 


3 


2 


2.9 


f 


i* 


0.98 


3-9 


3 


4 


3 


2 


3 





2.8 


1 


ItV 


1. 10 


4.0 


3 


6 


■3 


4 


3 


2 


3-0 


1 


li 


1. 17 


4.1 


3 


7 


3 


5 


3 


3 


3-1 


I 


li 


1.30 


4.4 


3 


9 


3 


7 


3 


5 


3-3 



Joints proportioned as above range, in their " efficiencies," 
from 40 to 60 per cent in the single-riveted seams, and from 
60 to 80 per cent for double-riveting ; the smallest rivets and 
thinnest plates giving the smallest, and the larger work the 
largest, values. The average efficiencies may be taken as 
follows: 

Single-riveting : 

Size of rivet -3-^ | ^'^ -J f | | i 

Efficiency 55 55 53 52 48 47 45 43 

Double-riveting • 

Efficiency 75 73 72 71 67 66 64 63 



I20 THE STEAM-BOILER. 

The strength of a seam is obtained by multiplying the 
resistance of the solid sheet by the efficiency of the joint. 

The strength of well-made joints, as exhibited by test, in 
proportion to strength of the original plate, according to Clarke, 
are for plates f-inch thick and less, for the best English York- 
shire iron: 

Working- Strength. 

Original strength of plate loo ii,ooo lbs. per sq. inch. 

Single-riveted lap-joint 60 6,700 " " 

Double-riveted lap-joint 72 8,000 " ** 

Double-riveted butt-joint 80 9,000 " " 

Fairbairn found the strength of joints to be as follows: 

Strength of plate 100 Bursting tension. 34,000 lbs. 

Double-riveted joint 70 Proof tension .. . 17,000 " 

Single-riveted joint 56 Working tension. 4,250 " 

the working tension being taken as \ of the bursting tension. 
For cast-iron pipes the working tension may be estimated at \ 
the bursting pressure, and at about 

16,500 lbs. per sq. inch for bursting tension, 
5,500 *' " " " proof tension, 

2,750 *' " " " working tension. 

Welded joints for boilers have, if perfect, the same strength 
as the original plate, but they are apt to be uncertain. 

The thickness of plates is limited for best work. Very thin 
plates cannot be well calked, and thick plates cannot be safely 
riveted. The limits are about \ of an inch for the lower limit, 
and f of an inch for the higher limit. The riveting machine 
only can be used for very thick plates, a thickness of half an 
inch being about the limit of hand-riveting. 

In some cases the seams of the shells or the flues of boilers 
are put together in helical form, and some increase of strength 
is thus secured in the longitudinal at the expense of the girth- 
seams. If 71 represent the ratio of the projected length of the 
seam on the circumference to the corresponding length of the 



MATERIALS— STRENGTH OF THE STRUCTURE. 



121 



projection longitudinally, the ratio of strength, as compared 
with the common seam, is measured by the ratio 




2;r 



fn 



n' + 2 



For, in Fig. 6y, let ABC represent a part of a sheet 
on which the diagonal AC is the line of the joint; 
AB is the corresponding longitudinal joint, as com- 
monly made, and BC the girth seam. 

Then the stress per unit of length 
of AB will be unity ; that on BC will 
\ be 2, and the total stresses will be, 
respectively, 2 and n, where 7t meas- 
ures the ratio of BC to AB, or the 
" rake" of the seam. The total re- 
sultant stress will be BE on the joint 
AC, and its normal component will 
be BE, the sum of the components 
of those on the longitudinal and 
girth seams, AB and BC, resolved 
perpendicular to AC, and the in- 
tensity of that stress is the quotient 
of this sum divided by the length, AC, of the seam. Hence 
the intensity on AB will be 



Fig. 67. 



2XAB 
'^ = -AB- = ^ 



that on BC will be 



t.= 



nAB 



= i; 



that on AC will be 



t^ = 



2 sin 6 -\- n cos 6 

Vi + n' 



122 THE STEAM-BOILER. 

But 

Sin 6 = -— ; cos 6 = 



and 



Vi+n'' Vi i-n'' 



^3 ^^ \ 2 ^I^d -J- = 5 \ 



When n is given the values below, the ratios of strength of 
seam are as tabulated. 



STRENGTH OF HELICAL SEAM. 



(Common longitudinal seam = i.) 



n m 

I.O 

i 1.3 

1 1.4 

1.25 1.5 

1.5 



n m 

1.75 1.6 

2. GO 1.7 

3.00 1.8 

CO 2.0 



When n =^ o the joint is parallel with the axis of the cylin- 
der ; it becomes a longitudinal seam. When ;2 = 00 , it becomes 
a girth-seam of twice the relative strength. When the angle of 
"rake" is 30°, the gain is 10 per cent; when 45°, the gain be- 
comes 0.4. It is obvious that this form of seam is very waste- 
ful of metal, if so much inclined as to secure any considerable 
gain of strength, if the boiler or the flue is built of a succession 
of ring courses laid side by side ; in such constructions as Root's 
" spiral pipe," in which the courses are helical, this objection 
does not hold. 

The '' factor of safety," as stated where reference is made to 
the strength of steam-boilers, is usually misleading, as, for ex- 
ample, in the U. S. regulations. Pressures one sixth those 
computed from the reports of tests of strength of the plate are 
permitted ; but the real factor of safety is obtained by multi- 
plying this nominal factor by the coefficient of strength of seam. 
Thus, where the law allows six the real factor is 0.56 X 6 = 3.36 



MATERIALS— STRENGTH OF THE STRUCTURE. 1 23 

for the single-riveted seam, or 0.7 X 6 = 4.2 for double-riveting, 
Fairbairn's coefficients being accepted. The real factor should 
not be less than six, and some authorities, following Rankine, 
would make it eight, and others even ten. 

51. Punched and Drilled Plates usually differ in strength, 
but each may be either stronger or weaker than unperforated 
metal of equal area of fractured section. When the metal is 
very soft and ductile, the operation of punching does no appre- 
ciable injury, and the Author has sometimes found it actually 
productive of increased strength, the flow of particles from the 
hole into the surrounding parts causing stiffening and strength- 
ening. With most steel and with hard iron the effect of 
punching is often to produce serious weakening and a tendency 
to crack, which has in some cases resulted seriously. With 
metal of the first class, punching is perfectly allowable ; with 
iron or steel of the second class, drilling should always be prac- 
tised. It is customary, in the practice of the most reputable 
engineers and builders, to drill all steel plates, but usually to 
punch iron. Sometimes the steel plate is punched with a 
punch of smaller diameter than the proposed rivet, and is sub- 
sequently reamed out or counterbored to size. It is generally 
assumed that this method is perfectly safe. 

Messrs. Greig and Eyth, after a long and carefully con- 
ducted investigation, say:* 

" The experiments show that the plates invariably lose part 
of their tensile strength in the section of solid material left 
between the rivets of a seam, this loss being greatest in lap- 
joints. It is also greater in punched than in drilled plates 
(iron as well as steel), and greater in plates riveted together by 
steam, than in those riveted by hydraulic pressure. On the 
other hand, the strength of rivets against shearing is greater 
than its normal figure, especially in lap-joints. 

'' The usefulness of double-riveting appears to be mainly 
due to the fact that it more effectually prevents lap-jointed 
plates from bending under stress. At the same time the zig- 
zag riveting generally adopted, in double-riveting, increases 

* Lond. Enginee?ing, June 29, 1879. 



124 THE STEAM-BOILER. 

the tensile resistance of the material between the rivets con- 
siderably beyond its normal figure. 

'' Butt-joints, with a cover on one side of the plate only, 
gave no advantage at all, the cover behaving simply as an 
intermediate plate attached to the two main pieces by an ordi- 
nary lap-joint. A marked improvement could, no doubt, be 
obtained by giving the cover greater thickness, so as to prevent 
its bending. 

''The most effective seams, as to tensile strength, were 
butt-joints with two covers, as not only do they nearly double 
the shearing strength of each rivet, but they entirely prevent 
the bending of the main plates. The main fact resulting from 
the tests of parts of boilers and complete boilers under hy- 
draulic pressure was the impossibility of bursting an ordinary 
rivet-seam in this way, the compression of the rivet and the 
elongation of the rivet-hole resulting invariably in leakage,, 
which prevented the necessary pressure from being obtained.. 
Each rivet becomes its own safety-valve, and the strain put on 
the weakest part of the structure never reached more than Jo 
per cent of the breaking strain. This is the point where addi- 
tional hardness of the material would be most useful, as it 
would prevent the opening of the rivet-holes, which now makes 
a boiler useless long before the breaking strain is reached." * 

Good steel is much more enduring than any iron, both 
against ordinary wear and extraordinary strain. 

The results of experiments on the best British steel for 
ship-building and for boilers, as reported to Lloyds, show that 
the injury done by punching is less as the plates are thinner, 
amounting, in the cases reported, to less than lo per cent in 
sheets J inch (0.6 cm.) thick, and rapidly increasing, becoming 
20 per cent at f inch (i cm.), and is still more serious with the 
heavy plate used for large ships and for boilers. But the injury 
was discovered to be local, and confined to a shell lining the 
punched hole, and but about one eighth of an inch (0.3 cm.) in 
thickness. This can be readily cut out, and the punched and 
counterbored, or reamed, holes produce no observable weak- 

* Lond. Engineering, 1879. 



MATERIALS— STRENGTH OF THE STRUCTURE. 12$ 

ness. In many instances no special precautions are taken in 
this direction where the metal is less than one half inch (1.25 
•cm.) in thickness. 

'52. Hand-riveting and Steam-riveting are both prac- 
tised by good makers, and authorities are somewhat divided in 
opinion as to their relative merit. With either system, good 
work may be done by a good workman ; by either method, 
-dangerously defective boilers may be produced. With a prop- 
erly designed riveting rriachine of the right size for its work, 
and carefully manipulated, very perfect work may be done. 
Careless handling produces distorted rivets, eccentrically placed 
heads, and sometimes causes the formation of a " fin" on the 
rivet, which, entering between the sheets to be riveted to- 
gether, holds them apart and causes leakage along the seam. 
When the plates are well adjusted, in metallic contact, and per- 
fectly secured, before the rivet is " headed up," this last defect 
is not likely to appear. The careful adjustment of the rivet- 
head to the die which supports it against the blow of the ma- 
chine, and the exact alignment of rivet and striking die, will 
prevent distortion of the rivet by the blow. Sometimes the 
machine is too light for its work ; in such cases two blows may 
be necessary to completely form the head and to expand the 
body of the rivet sufificiently to fill the rivet-hole. 

In hand-riveting the action of the hammer often hardens 
the metal in the head, and gives it such rigidity and brittleness 
that it may even fly off at the last stroke of the riveting ham- 
mer. The cone-shaped head is a comparatively weak form, and 
it is better to use a cup-shaped die, or former, and a larger 
liammer striking fewer and heavier blows, to form a hemi- 
spherical head, which latter is much stronger, and neater in 
appearance. Work of this kind may be quite as good as the 
best machine-riveting, but it is usually — not invariably — more 
-costly. 

Riveting machines constructed with two dies moved inde- 
pendently^the one a hollow die, having for its office the closing 
up of the lap simply; the other a solid die, which immediately 
follows up the first and sets up the rivet — are probably much 
better than the more comm.on form of riveter having one die 



126 THE STEAM-BOILER. 

only. Messrs. Greig and Eyth found the following to be the 
pressures attained on the heads of f-inch steel rivets :* 

Lbs. 

Steam-riveter 82,380 

Hydraulic stationary 86,360 

Hydraulic portable 44,018 

Power light blow 69,384 

Power heavy blow 115 ,640 

The best work was done by the steam-riveter. 
They conclude that — 

" The well-known fact of the superiority of riveting by 
machinery over hand-riveting has been again demonstrated 
most conclusively, while the experiments have shown that the 
effects of steam-riveting is, to say the least of it, not inferior 
to hydraulic riveting as far as the quality of the rivet is con- 
cerned, but that the hydraulic riveting is distinctly superior as 
to its effects on the plate, which is less injured by the slow 
pressure of the hydraulic ram. 

'' Steel showed in this respect a decided superiority over 
iron beyond the proportion due to its greater tensile and shear- 
ing strength." 

The conclusions of Mr. J. M. Allen are that machine-rivet- 
ing probably results in a greater proportion of defective rivets 
than any other one cause. Machine-riveting to make good 
work must be very carefully done. The rivet-hole must be truly 
in line with the machine dies. The holes in the two plates 
must also be in line with each other. If there is an offset 
between them, the rivet is sure to be a very bad one. The 
most satisfactory riveting of boiler-plates is done by a prop- 
erly constructed and used button-set. By this means better 
and more rapid work can be done than by hand-riveting. A 
well-constructed machine will work quicker than the set, but 
we have rarely seen a complete job of machine-riveting which 
left nothing to be desired. It was not the fault of the machine^ 
however. In hand-riveting the excellence of the joint depends 

* Lond. Engineering , June 29, 1879. 



MATERIALS— STRENGTH OF THE STRUCTURE. 12/ 

Upon the form of the set. With an improper set it is impos- 
sible to do good work, no matter how skilful the .workmen 
may be. 

53. Welded Seams are considered better than riveted, 
where facilities for welding are provided such that the weld 
may be made with certainty and invariably perfect. Unless 
special and very complete arrangements are made for securing 
absolute metallic contact, a good welding heat without oxida- 
tion, and thorough union by pressure or impact, welds are very 
apt to prove exceedingly unreliable. A gas-furnace, with a de- 
oxidizing flame of large volume and covering a considerable 
length of seam, has done good work, and some makers are 
adopting this system to the exclusion of riveting. Large boilers 
are sometimes made without the use of a single rivet in any 
important line of junction. It seems possible, and even prob- 
able, that welding may in time displace riveting in all good 
boiler construction. 

54. " Struck-up" or Pressed Shapes are adopted, in pref- 
erence to riveted or even welded parts, wherever the form and 
size of the piece will admit. Dome-tops, manhole and hand- 
hole plates, and sometimes large tube or flue sheets, are thus 
made. The piece is made by compressing the sheet of which 
it is to be constructed between a pair of dies, and thus compel- 
ling it to take the shape of the intermediate space, which is that 
of the finished piece. The pressure is commonly applied by 
means of the hydraulic press. Small pieces are shaped in the 
drop-press, or drop-hammer, in which the dies are forced to- 
gether by the blow of a heavy " tup," or hammer, falling from 
a height of from two to six feet or more, according to the size 
and the intricacy of form of the part to be produced. 

55. Cast and Malleableized Iron, Brass, and Copper all 
have limited application in steam-boilers. 

Cast-iron is used in the construction of manhole plates, of 
some of the fittings, and even, in many instances, in the heads 
of plain cylindrical and flue boilers. Its use is, however, always 
to be deprecated where wrought-iron can be substituted. When 
it is adopted, in places in which it may be subjected to heavy 
loading, and where its failure may prove a serious matter, 



128 THE STEAM-BOILER. 

great care should be taken to secure the best possible quality. 
It would be advisable, probably, in such cases, to use '' gun- 
iron," as it is called, which is cast-iron of the best grades, melted 
in an ''air-furnace" — a reverberatory furnace — and refined by 
'' poling," or stirring with a pole, usually a birch sapling, until 
its quality and composition are satisfactory. No contact being 
allowed with the fuel or any flux or other source of contami- 
nation by phosphorus or other objectionable element, greater 
strength and toughness can be obtained than when the melting 
is done in a " cupola" furnace, in which the iron, fuel, and any 
flux that may be used are mixed together. The process is ex 
pensive ; but the product is correspondingly valuable, the tena- 
city of good gun-iron exceeding, often, 30,000 pounds per square 
inch (2109 kgs. per sq. cm.), and its elasticity and elastic resili- 
ence approximating similar properties in wrought-iron. 

Malleableized cast-iron is usually given application in small 
castings forming parts of the various attachments to boilers. 
It is made by selecting a free-flowing cast-iron, as light in grade 
as possible, making the castings in the usual way and then sub- 
jecting them to a process of prolonged annealing at a red heat 
in the presence of substances capable of abstracting the cafbon, 
such as iron-ore, blacksmith's scale, or other materials rich in 
oxygen. The abstraction of the carbon thus leaves the casting 
stronger, somewhat ductile and malleable, and, as a rule, a much 
safer material than when in its original state ; it has become a 
crude wrought-iron. Only small pieces can be successfully 
made in this manner, except by annealing for days, or even 
several weeks ; the larger the casting the longer the time de- 
manded. Some so-called " steel-castings" are thus made. 

Brass and bronze are used mainly in the encasing of pres- 
sure-gauges, water-gauges, and similar appurtenances, in the 
construction of gauge and other cocks, and in valves and their 
seats ; it is less liable to be cut away by steam, or by water, 
and hence brass valves keep tight longer than do iron valves or 
cocks. Bronze is better than brass, but its higher cost precludes 
its general use. Muntz metal, which consists of copper 60, zinc 
40, and gun-bronze, 90 copper and 10 tin, are the most generally 
useful compositions ; but the brasses in common use generally 



MATERIALS—STRENGTH OF THE- STRUCTURE. I2g 

contain more or less of lead, and the bronzes are often also 
similarly adulterated. For surfaces exposed to friction the 
addition of lead is thought by many to be an advantage. The 
strongest of all such alloys is that consisting of copper 43, zinc 
55, and tin 2, or one having a somewhat less proportion of tin; 
this has been called by the Author, its discoverer,''^ " maximum 
bronze." The presence of zinc or other foreign element in the 
real bronzes is found to be particularly objectionable in those 
alloys intended for use in salt water, as it renders the latter 
especially liable to injury by local and rapid corrosion. 

56. The Strength of the Shells and Flues of boilers may 
be readily calculated when the data can be safely relied upon. 
The two forms are subject to quite different laws, however ; and 
even the strength of cylinders subjected to internal pressure, as 
are the cylindrical shells of steam-boilers, when thick, is calcu- 
lated by different methods from those applicable when of thin 
plate ; but it is not asserted that the heavy shells of large 
marine boilers, in which the metal is from three quarters to, 
sometimes, above an inch thick, may not be properly calculated 
by the rule applying to thick cylinders of cast-iron or other 
non-ductile material. 

Cylindrical Boiler-Shells, and other thin cylinders, have a 
thickness which is determined by the tenacity of the metal and 
the character of the riveted or other seam. If/ be the internal 
pressure, T the mean tenacity to be calculated upon along the 
weakest seam, r the semidiameter, and t the thickness, we have 
for axial stresses for equilibrium, 

pnr'' — 27trtTy 
and 

2tT pr 
p^ ; / = ^ (i) 

But for transverse stresses tending to rupture longitudinal 
seams, 

pr = tT, 

* See " Materials of Engineering:" The Alloys- 
9 



130 THE STEAM-BOILER. 

and 



tT pr 

p = -y; t=^-^. ...... (2; 



With seams of equal strength in both directions, therefore, 
the cyhnder is at the point of rupture along the longitudinal 
seams, while capable of bearing twice the pressure on girth 
seams. It is evident that spheres have twice the strength of 
cylinders of equal diameter. 

Thick cylinders are considered later, as they are usually 
made in cast-iron. 

Flat Boiler-heads are made both in wrought and cast iron. 
For these Clark's rules may be used.* 

For elastic deflection, 

"=5 « 

For maximum pressure, 

tT 
/ = o.2i5-T-, (4) 



or, for iron, 



For steel. 



For cast-iron, 



< 



p = IO,OOOj. . (5) 



/= 11,500^^ (6) 



/ = 4,000^, (7) 



when t is the thickness, d^ the diameter, both In inches,/ the 
pressure and T the tenacity, both in pounds per square inch. 

* Inst. C. E., vol. liii.. Abstracts. London, 1877-7S. 



MATERIALS— STRENGTH OF THE STRUCTURE, I3I 
For spherical ends, 

P=^—1T-. (8) 



4v-{-v 



where a is 108,000 for wrought-iron, 125,000 for steel, 45,000 
for cast-iron, and v is the versed sine or rise of the head. 
Lloyd' s Rule for cylindrical shells of boilers is 

abt 

. p = ^' • • (9) 

in which ^ is a constant, 155 to 200 for iron and 200 to 260 for 
steel, b the percentage of strength of solid sheet retained at the 
joint, t is the thickness of the plate, and d the diameter of the 
shell. The value of b is thus reckoned {n = number of rows of 
rivets) : 

if = 100-^ •', for the plate ; 

Pi 

fid 
b = 100 — \ for rivets in punched holes ; 

b = 90 — , for rivets m drilled holes. 



The least of these values is taken. Here/j is the pitch of rivets, 
4i^ is their diameter, a^ is the area of the rivet-section. When 
in double-shear, i.ys^i is taken ior a^. The factor of safety is 
taken at 6, and boilers are tested by water-pressure up to 2/. 

The iron is expected to have a tenacity of at least 21 tons 
per square inch; steel must bear 26 tons (3307 to 4095 kilogs. 
per sq. cm.). 

Welds are found, when well made, to carry 75 to 85 per 
cent of the strength of the sheet. 

Steam-pipe is usually made with an enormous excess of 



132 THE STEAM-BOILER, 

strength to meet accidental stresses, such as those due to 
motion of water within them. The Author has tested pipes 
broken by '' water-hammer," as the engineer calls it, to looo 
pounds per square inch (70 kilogrammes per sq. cm.) after it 
had been thus cracked in regular work in a long line, while 
the steam-pressure was less than 100 pounds (7 kilogs. per sq. 
cm.). They had all been previously tested to about one third 
this pressure. 

Cylinders of cast-iron, for steam-generators or for steam- 
engines, are usually given a thickness greatly in excess of that 
demanded to safely resist the steam-pressure ; often, according 
to Haswell, 

for vertical cylinders, where d is the internal diameter, and 






for horizontal cylinders of considerable size. 

In metric measures, kilogrammes and centimetres, these 
formulas become 

i = -^A , nearly; (i2> 

200 '3 -^ ' ^ ^ 



If r^ is the external and r^ the internal radius, Z'the tena- 
city of the metal, / its thickness, and/ the intensity of the in- 
ternal pressure, we have, for the thin cylinder, as an equation 
for equilibrium, 

pr^ = T(r, — r,) = Tt, nearly, . . . . (14) 



1 



I 

i MATERIALS— STRENGTH OF THE STRUCTURE. 1 33 

! and 

I Tt , , 

I . ""^"z' ^'^^ 

/=r.-r,=^; (i6) 

! 

P = T ('^) 

For the thick cylinder, however, the resistance at any inter- 
nal annulus of the cyhnder is less than T. 

Thick Cylinders, technically so called, are those which are 
of such thickness that the mean resistance falls considerably 
below the full tenacity of the metal, as exhibited in thin cylin- 
ders, in low-pressure steam-boiler shells, for example. Such 
cylinders are seen in the ''hydraulic" press, and in ordnance. 
I Barlow"^ assumes the area of section unchanged by stress, 

although the annulus is thinned somewhat by linear extension. 
If this is the fact, as the tension on any elementary ring must 
I vary as the extension of the ring within the elastic limit, the 

i stress in such element will be proportional to the reciprocal of 

the square of its radius, i.e., it will be 



/oo i; , (i8) 



and, taking the total resistance as/V,, when /' is the internal 
fluid pressure, since the maximum stress at the inner radius is 
7", that on the inner elementary annulus is Tdx, and on any 

other annulus — ^ dx ; while the total resistance will be, on 

X' 

either side the cylinder, 

p,r^ = 7>/ / — ^ = T p- '-— = T — — -. (19) 

^^2 x^ r, + {r^ — r^) r^+ t ^^ 

* Strength of Materials, 1867, p. 118. 



134 THE STEAM-BOILER, 

The maximum stress is at the interior, and may be equal, 
as taken above, to the tenacity, 7", of the metal ; then 



^=~t'= — J—' (20) 



and the thickness 



t = 4^ (21) 



while the ratio of the radii 



A ■ A T-p, 



• (22) 



Lmnfs Formula, which is more generally accepted, and 
which is adopted by Rankine, gives smaller and more exact 
values than that of Barlow. In the above, no allowance is made 
for the compressive action of the internal expanding force upon 
the metal of the ring. The effect of the latter action is to 
make the intensity of pressure at any ring less than before by 
a constant quantity, 

a . 
P^ p - ^, 

and the tension by which the ring resists that pressure greater. 



/oo J + ^. 



When r = ^1, / = o ; when r = r^, p = p^; 



then /i = —2 — b, and o — —^ — b\ 
^2 '1 



2 2 
r,r^ 



MATERIALS— STRENGTH OF THE STRUCTURE. 135 

and the maximum possible stress on the inner ring is 



r' 



^PA-' 






r,' + r/ 

^=/.r^ — f^5 (23) 



^■ = ^;:?^= (^4) 



and the ratio of inner and outer radii is 



/T+A 



(25) 



Of these two formulas, the first gives the larger and conse- 
quently safer results, and, in the absence of certain knowledge 
of the distribution of pressure within the walls of the cylinder, 
is perhaps best. 

For thick spheres, Lame's formula becomes 

2{r: - r:) 
/i = -^ ^ 3 _ ^^ 3 (20) 






Clark's formula* is more recent than the preceding. It is 
assumed that the expansion of concentric rings into which the 
cylinder may be conceived to be divided is inversely as their 
radii, and that the curve of stress will become parabolic if so 
laid down that the radii shall be taken as abscissas and the 
stresses as ordinates, the total resistance thus varying as the 

* Rules and Tables, p. 687. 



136 THE STEAM-BOILER. 

logarithm of the ratio of the radii. Then if the elastic Hmit be 
coincident with the ultimate strength, and 

T = the tenacity of the metal, 

R = the ratio, external diameter divided by internal, 

/ = the bursting pressure, 

/ = r X hyp log ie ; (28) 

R = e^ (29) 

In other cases, instead of Z take the value of the resistance 
at the elastic limit, and base the calculation of proportions upon 
the elastic limit and its appropriate factor of safety. The for- 
mulas as given are considered applicable to cast-iron. 

The strength of thick cast cylinders with heads cast in may, 
however, sometimes be far in excess even of the calculated re- 
sistance of thin cylinders. The formulas for thick cylinders 
appear to be in error on the safe side ; and very greatly so 
when, as is usually the case, the cylinder is short, and strength- 
ened by having a head cast in. Such cylinders are generally 
also strengthened by very heavy flanges at the open end. 

The Pressure allowed by Law or by government regulations 
on any cylindrical shell is found by the following rule : 

*' Multiply one sixth (-^) of the lowest tensile strength found 
stamped on any plate in the cylindrical shell by the thickness — 
expressed in inches or parts of an inch — of the thinnest plate 
in the same cylindrical shell, and divide by the radius or half 
diameter — also expressed in inches — and the sum will be the 
pressure allowable per square inch of surface for single-riveting, 
to which add 20 per centum for double-riveting." 

The hydrostatic pressure applied under the above table and 
rule must be in the proportion of 150 pounds to the square 
inch to 100 pounds to the square inch of the working pressure 
allowed. 

The following table gives the pressures thus calculated for 
single-riveted boilers of various sizes : 



MATERIALS— STRENGTH OF THE STRUCTURE. 



137 



TABLE OF PRESSURES ALLOWABLE ON BOILERS MADE SINCE FEB- 
RUARY 28, 1872. 







45,000 Ten- 


50,000 Ten- 


55,000 Ten- 


60,000 Ten- 


65,000 Ten- 


70,000 Ten- 




. 


sile 


sile 


sile 


sile 


sile 


sile 


v.* 


en 


Strength. 


Strength. 


Strength, 


Strength. 


Strength. 


Strength. 


'0 


03 




h 7,500 


^,8,333-3 


i, 9«i66.6 


B, 10,000 


i 10,833-3 


i, 11,666.6 












. 




«- 


1 --• 




. 


"o 






c'rt 




G --« 




c'rt 




c'rt 


1 c rt 




crt 








£ G 




5 c 




S c 




<u C 


a; c 




Z c 


s 


1 


t 


u.o 


3 


y.o 


«3 


:::i 


3 


00 


ure 

:r c 
itio 


3 


".2 


p 


ii. 




4) '-a 


CO 


lU'-o 




IUT3 


1 


(U'-O 


in a^-a 


OQ 


aj-O 


.a 

x: 
H 





(0 


? 


P^ 


7 


7 




I 


7 




1875 


78.12 


93-74 


86.8 


104.16 


95.48 


"4-57 


104.16 


124.99 


112.84 135-4 


121.52 


145-82 




21 


87 


5 


105 




97.21 


116 


65 


106.941128.3 


116 


66,139.99,126.38 151 


65 


136.11 163.33 




23 


95 


83 


114 


99 


106.47 


127 


76 


117. 12 


140.54J127 


771153.321138.41 166 


09 


149. 07 1 178. 88 




25 


104 


16 124 


99115-74 


138 


88 


127.31 


152.77 138 


88;i66. 65 150.46 180 


55 


162.03^193.43 


36 


26 


108 


33 129 


991120.37 


144 


44 


132.4 


158. 88,144 


44:173.321156.48 187 


77 


168.51 202.21 


Inches. 


29 


120 


83144 


99 


134-25 


161 


IX 


147.68 


177.21 i6i 


11:193-33,174-53 209 


43 


187.90 225.48 




3125 


130 


2 


156 


24 


144.67 


173 


6 


15914 


190.96:173 


6 1208.321188.07 225 


68 


202 5 243.04 




33 


137 


5 


165 




152.77 


183 


32 ; 168 . 05 j 201 . 661 183 


33;2i9.99!i98.6i 238 


33 


213.88 256.65 




35 


145 


83 


174 


99 


162.03 


194 


431I78.23 


213.87 


194 


44'233-32 


210.64 252 


76 


226.84 


272.20 




375 


156 


I:!!l 


5 


173.61 


208 


33,190-97 


229.16 


208 


33|249-99 


225 69 271 


82 


243-05 


291.66 




1875 


74 


01' 88 


89 


82.23 


98 


67 90.46 


108.54 


^ 


68 118.41 


106.9 128 


28 


"5-13 


138.16 




21 


82 


89 i 99 


46 


92 I 


no 


521101.31 


121.57 


no 


52:132.621119 


73 143 


67 


128.93 


154-71 




23 


90 


78 108 


93 


100.87 


121 


04 110.96 


133-15 


121 


05,145.26:131 


13 157 


35 


141.22 169.46 




25 


98 


68 118 


41 


109.64 131 


56:120. 61J144. 73 


131 


57 157.88 142 


54 171 


04 


153.5 184.20 


38 


26 


102 


63' 123 


15 


114.03 136 


83 125-43:150. 511136 


84 164.2 148 


24 177 


88 


159.64 191.56 


Inches. 


29 


114 


47,137 


36 


127.19J152 


62 139.91 167.89 152 


63 183.15 165 


35198 


42 


178. 061213.67 




3125 


123 


35 148 


02 137. 1164 


46 150. 761180.91 164 


47 197- 36' 178 


17 213 


8 


191.88,230.25 




33 


130 


26 156 


31:144-73 173 


67 159.2 191.04I173 


68 208. 41 1188 


15 225 


78 


202.62 243. 14 




35 


138 


15 165 


78 153-5 184 


21 168.85 202. 62; 184 


21 221.05:199 


56239 


47 


214.91 257.89 




375 


148 




177 


60 164.73J197 


67 


180.81 


217.09 


197 


36 


236.83 213 


81256 


57 


230.26 276.31 




1875 


70 


31 


~87 


37 


78.12I 93 


74 


85-93 


103. II 


93 


75 


112. 5 


101 


56 121 


87 


109.37 131-24 




21 


78 


75 


94 


50 


87.49 104 


98 


96.24 


115.48J105 




126. 


"3 


74 136 


48 


122.49 146-98 




23 


86 


251103 


5 


95-83'ii4 


99 105.41 


126.49 115 




138. 


124 


58 149 


49 


134.16,160.99 




25 


93 


75I112 


5 


104.16 124 


99 ii4.58'i57.49'i25 




150. 


135 


41 162 


49 


145-83 174-99 


40 


26 


97 


5 J117 




108.33I129 


99 119.16 142.99 13d 




156. 


140 


83 168 


99 


151.66 181.99 


Inches. 


29 


108 


75 130 


5 


120.83:144 


99, 132.911159. 49:145 




174. 


157 


08 188 


49 


169.16 202.99 




3125 


117 


18 140 


61 


130.2 156 


24143. 22 


171.861156 


25 


187-45 


169 


27 203 


12 


182.29 218.74 




33 


123 


751148 


5 


137.49 164 


98151.24 


181. 481165 




198. 


.78 


74,214 


48 


192.49 230 98 




35 


131 


25 157 


5 


i45-83|i74 


99I160.41 


192,-491175 




210. 


189 


58227 


49 


204.16:244.99 




375 


140 


62 168 


74 


156.24 


187 


48 


171.87 


206 . 24 


187 


5 


225. 


203 


12 243 


74 


218.74262.48 




1875 


(^(> 


96 80 


35 


74.40 


89 


28 


81.84 


98.20 


89 


28 107.13 


^ 


72 116 


06 


104.16 124.99 




21 


75 


90 




83 32 


99 


99 


91.66 


109.99 


100 


|l20. 


108 


33! 129 


99 


116.66,139.99 




23 


82 


14; 98 


56 


91.23 


109 


51 


100.39 


120.46 


109 


52 131.42 


118 


65 142 


38 


127.771153 32 




25 


89 


28 107 


13 


99-2 


119 


04 


log . 12 


130.94 


119 


04 142.84 


128 


96 154 


75 


138.88 


166.65 


42 


.26 


92 


85 III 


42 103.17 


123 


g 


113-49 


136.18 


123 


8 :i48.56 134 


12,160 


94 


144.44 


173-32 


Inches. 


29 


103 


57 124 


28115.07 


138 


08 


126.57 


151-85138 


09165.7 149 


6 !i79 


52 


161.11 


193-33 




3125 


III 


6 133 


92 124. 


148 


8 


136.4 


163.68 148 


74 178.56161 


2 !i93 


44 


173.61 


208.23 




33 


117 


85I141 


42,130. 94'i57 


12I114.04 


172.84 157 


14 188.56 170 


23 204 


27I183-33 


219.99 




35 


125 




150 


1 138. 88 


166 


65 152.77 


I83.32JI66 


66,199.991180 


55 216 


66:194.44:233.32 




375 


133 


92 


160 


7 


148.8 


178 


56 


163.68 


196.40 


178 


57 214.28 


193 


45232 


14 


208.33 249 99 




1875 


63 


92 


"^ 


7 


71.01 


"sT 


22 


78.12 


93-74 


85 


22 102.26 


92 


32 no 


'^l 


99.42I119.3 




2t 


71 


59! 85 


9 


79-54 


95 


44 


87.49 


104.98 


95 


45 "4-54 


103 


4 ,124 


08 


III. 36 133 


63 




23 


78 


4 94 


08 87.12,104 


54 


95-83 "4-99 


104 


54 125.44 


"3 


25 


135 


9 


121.96 146 


35 




25 


85 


22 102 


26, 94.69:113 


62 


104.16 124.991113 


63 n6.35 


123 


I 


147 


72 


132.56 159 


07 


44 


26 


88 


63 106 


35 98-48,118 


17 


108.33 129.90! 1 18 


18 141.81 


128 


02 


153 


62 


137.87 165 


44 


Inches. 


29 


98 


86 118 


63 109.84 131 


801120.83 1144. 99 131 


81158. 17 


142 


79 


171 


33 


153.78,184 


53 




3X25 


106 


53 127 


83 118.36 142 


03 130.2 1156-24 142 


04 170.44 


153 


88 


184 


^l 


165.71 198 


85 




33 


112 


5 135 


ii24.99;i49 


98 137. 49^164. 981150 


180. 


162 


49 


194 


f 


174.99 209 


98 




35 


119 


31 ^43 


17 132.57 159 


08^145.83 174 99I159 


09 190.9 


172 


34 


206 


8 


185.6 222 


72 




375 


127 


81 


153 


37 


142.04 


170 


44 


156.24 


187.48 


170 


45 


204.54 


184 


65 


221 


58 


198.86 


238 


63 



138 



THE STEAM-BOILER. 



TABLE OF PRESSURES ALLOWABLE ON BOILERS MADE SINCE FEB- 
RUARY 28, r^-j-2.— Continued. 







45,000 Ten- 


50,000 Ten- 


55,000 Ten- 1 60,000 Ten- 


65,000 Ten- 


70,000 Ten- 






sile 


sile 


sile 


sile 


sile 


sile 


CQ 


« 


Strength. 


Strength. 


Strength. 


Strength. 


Strength. 


Strength. 





B, 7,500 


i 8,333.3 


\, 9,166.6 


\. 10,000 


1, 10,833.3 


i 11,666.6 






1 ^_. 
















cIS 


"o 






c ^ 




C ni 




c rt 




c'rt 




c rt 






'S 




t) c 




<u C 




(U c 




<u c 




<u c 




5 c 


5 

1) 


IS 


u 

3 



^•5 


1 


u_o 


t 


<j_o 


t 




i 


o_c 


ij 


u 




.M 




(U'-O 




lu'-o 




c;^ 




HJ-O 


VI 


(u'-a 




(u'-S 


-< 

2 


i 


0" 




"^ 


Ix 


0« 


i 


"* 


(0 




^ 


T- 


Q 


H 


cu 


s 


Ph 


g 


Oh 





Oh 


8 


(X 


8 


a! 


% 




1875 


61.14 


73-36 


67-93 


81.51 


74.72 


89.66 


81.51 


97.81 


88.31 


105.97 


95-1 


114. 12 




21 


68.47 


82 


16 


76 


08I 91.29 


^3^9 


100 


42 


91-3 


109 


56 


98.91 


118.69 


106.52 


127.82 




23 


75- 


90 




83 


33 100. 


91. 66; 109 


99 100. 


120 




108.33 


129.99 


116.66 


139-99 




25 


I'^-^l 


97 


81 


90 


57 108.68 


99.63I119 


55 1 108. 69 J 130 


42 


117-75 


141-3 


126.8 


152.16 


46 


26 


81.78 


101 


73 


94 


2 113-04 


103.621124 


34,113.44,135 


64 


122.46 


146.95 


131.88 


158.25 


Inches 


29 


94-56;n3 


47 


105 


07 126. 


115-57:138 


68:126.09 151 


3 


136.59 


163.92 


147-1 


176.52 




3125 


101.9 


122 


28113 


21 135.86 


124.54 149 


44| 135.86 163 


03 


147-19 


176.62 


158.51 


190.21 




33 


107.6 


129 


12 119 


56 143-47 


131-52,157 


82I143 97172 


16 


155-43 


186.51 


167-39 


200.86 




35 


11413 


136 


95!i26 


8 152.16 


139.49,167 


38 152.17 182 


6 J164.85 


197.82 


i77-53'2i3-03 




375 


122.28 


146 


73 


135 


b6 163.03 


i49-45|i79 


34ji63. 04195 


64 176.62 


211.94 


190.21 228.25 




1875 


l^-|9 


7? 


30 


65 


I 78.12 


71.61 


85 


93 


78.12 93 


74 


84.63 


101.55 


91-13 


109-35 




21 


65.62 


78 


74 


72 


91 87.49 


80.2 


96 


24 


87.49 104 


98 


94-79 


"3-74 


102.08 


122.49 




23 


71.87 


86 


24 


11 


85 95-82 


87. 84! 105 


4 


95.83 114 


99 


103.81 


124.57 


III. 8 


133-16 




25 


78.12 


93 


74 


86 


8 104 16 


95-48,114 


57 


104.16 124 


99J112.84 


135.4 


121.52 


145-82 


48 


26 


81.25 


97 


50 


90 


27 108.32 


99-3 I119 


i6iio8.33 129 


99 117.36 


140.83 


126.38 


151-65 


Inches. 


29 


90.62 108 


74I100 


69 120.82 


110.76 


132 


91 


120.83 144 


99ii30-9 


157.08 


140.97 


169.16 




3125 


97.65 117 


18:108 


5 130.2 


119-35 


143 


22 


130.21 156 


25 


141.05 


169.26 


151-9 


182.28 




33 


103.12,123 


74I114 


58 137-49 


126.04 


^5^ 


24 


137.5 ^165 




148.95j178.74 


160.41 


192.49 




35 


109.37I131 


24 121 


52 145-82 


133-67 


160 


4 


145.83 174 


99 


157.Q8I189.57 


170.13 


204.15 




375 


117.181140 


61 130 


2 J156.24 


143.22 171 


86 


156.25,187 


50 


169.27 


203.12 


182.29 


218.74 




1875 


52.08 


62 


49! 57 


871 69.44 


63-65! 76 


38 


69.44 82 


44 


75.23 


90.27 


81.01 


97.21 




21 


58.33 


69 


99 64 


81; 77.77 


71.29I 85 


54 


77-77 93 


32 


84.25 


101. 1 


90.74 


108.88 




23 


63.88^ 76 


65: 70 


98 85.17 


78.081 93 


69 


85.18,102 


21 


92.28 


110.73 


99-38 


119.25 




25 


69.441 83 


32! 77 


16, 92.59 


84.87 lOI 


84 


92.59111 


10 


100.3 


120.36 


108.02 


129.62 


54 


26 


72.22! 86 


66, 80 


24 96.28 


88. 27 1 105 


92 


96.29 115 


54 


104.31 


125.17 


112.44 


134-8 


Inches. 


29 


80.55! 96 


66 89 


5 107.40 


98.45;ii8 


14 


107.41J128 


88 


116.35 


139-62 


125-3 


150.36 




3125 


86.8 !i04 


16' 96 


44 115.72 


106.09 127 


30 


"5-55 138 


66 


125.38 


150.45 


135-03 


162.03 




33 


91.66 109 


99 lOI 


84 122.22 


112.03 134 


43|l22.22 146 


66 


132.4 


158.88 


142.59I171.10 




35 


97.22 116 


66::oS 


02 129.62 


118.82 142 


581129.62 155 


541140.43 


168.51 


151.23I181.47 




375 


104.16 


124 


99 "5 


74 138.88 


127.31 


152 


77 


138.88 166 


65 


150.46 


180.55 


162.03 


194.43 




1875 


46.87 


56 


24 


52 


08 


62.49 


57.29 


68 


74 


62.5 75 




67.7 


81.24 


72.91 


87-49 




21 


52.5 


63 




58 


33 


69.99 


64.16 


76 


99 


69.99: 84 




75.83 


90.99 


81.66 


97-99 




23 


57-5 


69 




63 


88 


76.65 


70.27 


84 


32 


76.66 91 


99 


83.05 


99.66 


89-44 


107.32 




25 


62.5 


75 




69 


44 


83 -.32 


76.38 


91 


65 


83-33! 99 


99 90.27I108.32 


97.22 


116.66 


60 


26 


65. 


78 




72 


22 


86.66 


79-44 


95 


32 


86.66 103 


99 93.88|ii2.65 


lOI.II 


121.33 


Inches. 


29 


72-5 


87 




80 


55 


96.66 


88.61 


106 


33! 96.66 115 


99 104.721125.66 


112.77 


135-32 




3125 


78.12 


93 


74 


86 


8 


104.16 


95.48:114 


57 104.18 124 


99 112.95 


135.54 


121 .52 


145-82 




33 


82.5 


99 




91 


66 109.99 


100.83 120 


99 109.99 132 


I119.16 


142.99 


128.33 


15399 




^5 


87.5 


105 




97 


22 116.66 


106.94 128 


32,116.66139 


99 126.38 


151.65 


136.11 163.33 




375 


93-75 


112 


5 


104 


16 124.99 


114.58 137 


49 125. 150 




135-41 


162.49 


145-83 175-99 




1875 42.61 


51 


13 


47 


34 


56.8 


52.07I 62 


49 56.81 68 


17 


61.55 


73.86 


66.28 79.53 




21 


47-72 


57 


26 


53 




63.63 


58.33! 69 


99' 63.63 76 


35 68.93 


82.71 


74.24 89.08 




23 


52-27 




72 58 




69.69 


63.881 76 


65; 69.69 83 


62: 75-5 


90.6 


8i-3i| 97-57 




25 


56.81 


68 


17 


63 


13 


75-75 


69.44 83 


32, 75.751 90 


90 82.07 


98.48 88. 37:106.04 


66 


26 


59-09 


70 


9 


65 


65 


78.78 


72.22 86 


66 78.781 94 


53 85.35 


102.42 


91.91,110.29 


Inches. 


29 


65.90 


79 


08 


73 


23 


87-87 


80.55 96 


66 87.871105 


44 95-2 


114.24 


102.52I123.02 




3125 71- 


85 


2 


l^ 


91 


94.69 


86.89 104 


16' 94 69 113 


62(102.58 123.09 


110.47 132.56 




33 


75- 


90 




83 


33 


99.99 


91 .66 109 


99! 99.99 120 


108.33 129.90 


116.66 139.99 




35 


79-56 


95 


47 


88 


f 


106.05 


97.22 116 


66106. |I27 


27 ii4.89;i37.86 


123.73I148.47 




375 


85.22 


102 


26 


94 


69 


113.62 


104.16 


124 


99 


113.62 136 


34 


123. 1 


147-72 


132.57 


i59'08 



yiATERIALS— STRENGTH OF THE STRUCTURE. 1 39 



TABLE OF PRESSURES ALLOWABLE ON BOILERS MADE SINCE FEB- 
RUARY 28, -lZ-jz.— Continued. 







45,000 


Ten- 


50,000 


Ten-I 


55,000 Ten- 


60,000 


Ten- 


65,000 Ten- 


70,000 Ten- 






SILE 


SILE 


sile 


SILE 


sile 


sile 


c 


% 


Strength. 


Strength. 


Strength. 


Strength. 


Strength. 


Strength. 


4) 

'o 





h 7,500 


i 8,333.3 


i9-i6G.6 


^, 10,000 


B, 10,833.3 


i 11,666.6 


CQ 












«-■ 




^_. 




^„- 




*-' "^ 


"o 






C "3 




c «s 




C rt 




c'c5 




^ 2 




c rt 








5 c 




C c 




dj C 




(U c 




u c 




<u c 


a 

Q 


c 


3 


u 


3 


w_o 


t 

s 


u_0 


t 


00 


i 

3 


o_o 


<J 


00 


^ 


1/3 


w'-o 




(U'-S 


m 






jj'-S 


m 


^■■s 




w'-S 






8" 


ol 


8" 




I 


7 


en 






7 




.1875 


39.06 


46.87 


43-4 


52.08 


47^74 


57.28 


52.08 


62.49 


56.42 


67.70 


60.76 


72.91 




.31 


43-75 


52.5 


48.6 


58.33 


53-47 


64.16 


58.33 


69.99 


63.19 


75-82 


68 05 


81.66 




•23 


47-91 


57^49 


53.24 


63-88 


58-56 


70.27 


63.88 


76.65 


62.21 


83 05 


74 53 


89.43 




•25 


52.08 


62.49 


57-87 


69.44 


63.65 


76.38 


69.44 


83-32 


75.22 


90.26 


81 


01 


97.21 


72 


.26 


54-16 


64.99 


60.18 


72.21 


66.2 


79-44 


72.22 


86.66 


78 24 


93.88 


84 


25 


105.10 


Inches. 


.29 


60.41 


72.49 


67.12 


80.54 


73-84 


88.60 


80.55 


96.66 


87.26 


104.71 


93 


98 


112.77 




•3125 


65.10 


78.12 


72.33 


86.8 


79-57 


95-48 


86.8 


104.16 


94-03 


112 83 


lOI 


27 


121.52 




•33 


68 75 


82.5 


76.38 


91-65 


84.02 


100.82 


91.66 


109.99 


99.3 


119.16 


106 


94 


128.32 




•35 


72.91 


87.49 


8r .01 


97.21 


89.11 


106.93 


97.22 


116.66 


105.32 


126.38 


113 


42 


136. 1 




•375 


78.12 


Q3-74 


86.8 


104. 16 


95.48 


i'4-57 


104. 16 


124.99 


112.84 


135-43 


121 


52 


145.82 




•1875 


36.05 


43.21 


40.06 


48.07 


44.07 


52-87 


48.07 


57-68 


52.08 


62.49 


56 


08 


67.29 




.21 


40.38 


48.45 


44.87 


53-84 


49^35 


59.22 


5^84 


64.60 


58.33 


69.99 


62 


82 


75.38 




•23 


44-23 


53^o7 


49-14 


58.96 


54-05 


64.86 


58.95 


70.76 


63.88 


76.65 


68 


80 


82.56 




•25 


48.07 


57.68 


53 41 


64.09 


58.76 


70.5 


64-4 


76.92 


69.44 


83.32 


74 


78 


89 73 


78 


.26 


50. 


60. 


55.55 


66.66 


66.11 


73-33 


66.66 


79-99 


72.22 


86.66 


77 


77 


93 32 


Inches. 


•29 


55 76 


66.91 


61.96 


74.35 


68.16 


81.79 


74-35 


89.22 


80.55 


96.66 


86 


75 


104. 1 




•3125 


60.09 


72.1 


66.77 


80.12 


73.45 


88.14 


80.12 


96.14 


86.8 


104 16 


93 


48 


112.17 




•33 


63.46 


76.15 


70.51 


84.61 


77-56 


93-07 


84.61 


101.53 


91.66 


109.99 


98 


71 


118.45 




•35 


67-3 


80.76 


74.78 


89 • 73 


82.26 


98.71 


89 74 


107.68 


97.22 


116.66 


104 


70 


125.64 




•375 


72.11 


86.53 


80.12 


96.14 


88.14 


105.76 


96.15 


"5-38 


104.16 


124.99 


112 


17 


134 6 




.1875 


33-48 


40.17 


37.2 


44.68 


40.92 


49 I 


44.64 


53-56 


48.36 


58.03 


52 


08 


62.49 




.21 


37-5 


45 • 


41.66 


49 99 


45-83 


54-95 


50. 


60. 


54.16 


64 99 


58 


33 


69.99 




•23 


41.02 


49.22 


45.63 


54.75 


50.19 


60.22 


54.75 


65 71 


59.32 


71.18 


63 


65 


76.38 




•25 


44.64 


53.56 


49.6 


59.52 


5456 


65-47 


59.52 


71.42 


64.48 


77.37 


69 


44 


83 32 


84 


.26 


46.42 


55.7 


51.58 


61.89 


56.74 


68 08 


61.9 


74.28 


67.05 


80.46 


72 


22 


86.66 


Inches. 


•29 


51-78 


62.13 


57-53 


69.03 


63-29 


75 94 


69.04 


82.84 


74-8 


89.76 


80 


55 


96.66 




.3125 


55-8 


66.96 


62. 


74.4 


68.2 


81. S4 


74.4 


89.28 


80.6 


96.72 


86 


8 


104.16 




•33 


58.92 


70.7 


65-47 


78.56 


72.02 


86.42 


78-57 


94.28 


85.11 


102. 13 


91 


66 


109.99 




•35 


62.5 


75 • 


69.44 


83.32 


76.38 


9f65 


83-33 


99-99 


90.27 


108 . 32 


97 


22 


116.66 




•375 


66.96 


80.35 


74 4 


89.28 


81.84 


98.2 


89.28 


107.13 


96.72 


116.06 


104 i6 


124.99 




•1875 


31-25 


37-5 


34-72 


41.66 


38.19 


45-82 


41.66 


49.99 


45-13 


54.15 


48.68 


58.33 




.21 


35- 


42. 


38.88 


46.65 


42.77 


51-32 


46.66 


55.99 


50.55 


60.66 


54.44 


65-32 




•23 


.38.33 


45-99 


42.59 


51.10 


46.85 


56.22 


51. II 


61-33 


55.37 


66.44 


59.62 


71-54 




•25 


41 .66 


49-99 


46.29 


55-54 


50.92 


6x.i 


55.55 


66.66 


60.18 


72.21 


64.81 


77-77 


90 


.26 


43-33 


51-99 


48.14 


57.76 


52 96 


63 55 


57-77 


69-32 


62.59 


75.1 


67.4 


80. 88 


Inches. 


.29 


48-33 


57-99 


53-7 


64.44 


59.07 


70.8 


64-44 


77-32 


69.81 


83-77 


75.18 


90.21 




•3125 


52.08 


62.49 


57.86 


69.43 


63.65 


76.38 


69.44 


83-32 


75.23 


90.27 


81.01 


97.21 




•33 


55- 


66. 


6t.ii 


73-33 


67.22 


80.66 


73.33 


87-99 


79-44 


95.32 


85.55 


102.66 




•35 


58.33 


69 99 


64.81 


77.77 


71.29 


85-54 


77.77 


93.32 


84.25 


101. 1 


90.72 


108.88 




•375 


62.5 


75- 


69-44 


83.32 


76-38 


91.65 


83-33 


99-99 


90.27 


108 . 32 


97.22 


116.66 




•1875 


29.29 


35-M 


32.55 


39.06 


358 


42.96 


39.06 


46.87 


42.31 


50.77 


45.57 


54-68 




.81 


32.81 


39-37 


36-45 


43.74 


40. :i 


48.12 


43 - 75 


52.5 


47.39 


■;6.86 


51.04 


61.24 




•23 


35.93 


43 . 1 1 


39-93 


47.91 


43-92 


52.7 


47.91 


57.49 


51-9 


62.28 


55-9 


67 08 




•25 


39.06 


46.87 


43-4 


52.08 


47.74 


57.28 


52.08 


62.49 


56.42 


67.67 


60.76 


72.91 


96 


.26 


40.62 


48.74 


45-14 


54.16 


49.65 


59-68 


54.16 


64.99 


58.78 


70.53 


03.19 


75.82 


Inches. 


•29 


45-31 


54 37 


50.34 


60.4 


55.38 


66.45 


60.41 


72.49 


65.45 


78.54 


70.48 


84-57 




•3125 


48 82 


58.58 


54-25 


65-1 


59-67 


71.6 


65.1 


78.12 


70.52 


84.62 


75-95 


or. 14 




•33 


51-56 


61.871 57.29 


68.74 


63.02 


75.62 


68.75 


82.5 


74-47 


89-36 


80.2 


96.24 




•35 


54-68 


65.61] 60.76 


72.91 


66.83 


80.19 


72.91 


87.49 


78.99 


94.78 


85.06 


102.07 




•375 


58.58 


70.29 


1 65.1 


78.12 


71.61 


85-93 


78.12 


93 74 


84.63 


101.55 


91 


.14 


109.6 



I40 THE STEAM-BOILER. 

Externally-fired boilers are not permitted by United States 
regulations to be made thicker than 0.51 inch (1.2 cm.). The 
20 per cent higher pressure of the table is allowed on steam- 
vessels which carry no passengers. It will be observed that 
the rule above given allows an apparent ** factor of safety" of 
six ; while the loss of strength at a single-riveted seam reduces 
it to the actual value of four, nearly. It would probably be on 
the whole wiser to use as the actual value the higher figure, 
and thus to reduce the pressures carried to one third below 
those now permitted, except where inspection and test during 
construction, and constant supervision with frequent inspection 
during the life of the boiler, may give a safe margin with the 
lower figure. The operation of the law which allows old boilers 
to carry two thirds the test pressure is to reduce the real factor 
often to less than one and a half ; for it is well known that 
iron will not carry permanently a load which it will sustain for 
a short time without observable yielding. 

French regulations make the thickness of wrought-iron 
cylindrical shells of boilers not less than 

t = \..%pd + 3 

in millimetres, when the pressure, /, is in atmospheres and the 
diameter, d, is in metres. In no case, however, is a greater 
thickness allowed than 1 5 mm. (0.6 in.). 
German regulations give 

t = o.ooi^pd ~\- 0.1 inches. 

Flues and Cylinders subjected to external pressure resist 
that pressure in proportion to their stiffness and their com- 
pressive strength if thin, and if thick sustain a pressure pro- 
portional to their thickness and maximum resistance to crush- 
ing. 

Fairbairn,* experimenting on flues of thin iron, 0.04 inch 

* Useful Information. Second Series. 



MATERIALS— STRENGTH OF THE STRUCTURE. I4I 

(0.102 centimetre), of small diameter, 4 inches (10.2 centi- 
metres) to 12 (31 centimetres), and from 20 inches (50.8 centi- 
metres) to 5 feet (1.52 metres) long, found that their resistance 
to- collapse varied inversely as the product of their lengths and 
their diameters, and directly as the 2.19 power of their thick- 
ness. 

The following equation fairly expressed his results when/ 
is the external pressure in pounds per square inch, / their thick- 
ness in inches, d their diameter, and L the length in feet : 



i—\ -^ ; p = 806,000^--; . . . . (i) 

V 806.000 ^ ' dL ^ ^ 



806,000' ^ ' dL' ' 

or, for the length in inches, 



/ = 9,672,000—-. ...... (2) 



In metric measures, kilogrammes and centimetres diameter, 
and metres of length, 

^2.19 
/ = 68,000—, nearly (3) 



= {ll±^- (4) 

V 68.000 • • • . ^^^ 



2d' 



For elliptical flues take d ^= -j-', where a is the greater and 

b the lesser semi-axis. 

These equations probably give too small values of / for 
heavy flues under high pressure. 

Belpaire's rule, deduced from Fairbairn's experiments, is 



p = i,oi7,iio^— (5) 



142 THE STEAM-BOILER. 

Lloyd's rule for flues is 



'-'-L («) 



in which a is made 89,600 pounds per square inch. 

The British Board of Trade Rule is, for cylindrical furnaces 
with butted joints, 

af 

^^JT+Yy^ ..-,.. (7) 

in which a is 90,000, provided, always, 



p < 8,000-^; 
a 



and for large joints a = 70,000, unless bevelled to a true circle, 
when a — 80,000. If the work is not of the best quality, these 
values of a are reduced to 80,000, 60,000, and 70,000. 

Flanged and Corrugated Flues are much stronger than plain, 
lapped, or butt-jointed flues. Experiment indicates that it is 
allowable to consider the length L in the formulae for strength 
of flues as the distance from flange to flange, and to assume 
that the flanges support the flue as effectively as the flue 
sheets. Where the several courses of a flue are flanged to- 
gether instead of being connected by the usual lap-jointed 
girth-seams, the strength of the flue is thus enormously in- 
creased. Another method of strengthening the flue is by sur- 
rounding it, at intervals, with a strongly made ring of angle or 
T-iron, which answers the purpose of a flange, while being less 
costly in construction. To prevent injury by overheating at 
those parts where the total thickness of metal traversed by the 
heat from the furnace-gases would be objectionably great, the 
ring is often supported clear of the flue by a set of thimbles 
through which the rivets holding it in place are driven. 

The corrugated flue is now very extensively used, the cor- 
rugations extending around the flue and having a pitch of ten 



MATERIALS— STRENGTH OF THE STRUCTURE. I43 

or twelve times the thickness of the sheet. These flues pos- 
sess the double advantage of having more than twice the 
strength of equally heavy plain flues, and of being so much 
thinner for a given strength as to be vastly safer against over- 
heating and burning. These flues are less liable to distortion 
in the processes of working than are plain flues. 

By the United States regulations, lap-welded flues less than 
18 feet long and 7 inches or more in diameter are allowed to 
carry pressures determined by the formula 

ct pr 

r c 

in which the pressure, /, is in pounds per square inch ; the 
thickness, /, and the radius, r, of the flue in inches. The value 
of the constant c is 44. This gives, for example, an allowable 
pressure of 200 pounds per square inch on a flue 14 inches in 
diameter, less than 18 feet long and 0.32 thick. A minimum 
thickness is set at 

t — 2.2d. 

For lap-welded flues exceeding 18 feet in length, 3 pounds is 
deducted from the pressure calculated as above, for each added 
foot, or o.oi inch is added to its thickness. When between 7 
and 16 inches diameter and 5 to 10 feet long, one strengthen- 
ing ring is required ; and where 10 to 15 feet long, two such 
rings, each of a thickness of metal at least equal to that of the 
flue, and 2\ inches or more in width. 

Flues 16 to 40 inches diameter are allowed by the United 
States regulations a pressure 

, . , , 1760 

in which/ = -4--, f = 0.31, or 
a 

P = 5678^, 



144 THE STEAM-BOILER. 

which allows lOO pounds per square inch on a xlue 20 inches in 
diameter and 0.37 inch thick. 

Corrugated furnace-flues are allowed to " carry" a pressure^ 



p,^ ^^'500'^' 



equivalent to 150 pounds on a flue 40 inches in diameter and 
0.5 inch thick. Other flues are allowed pressures determined 
by Fairbairn's formula, 

f 
p = 89,600-^, 

in which, however, L is in feet. Rings are fitted in such man- 
ner as to reduce the maximum tension on the rivets to 6000 
pounds per square inch of section. 

57. Stayed Surfaces and Stays and Braces are parts and 
members which, in steam-boiler design and construction, should 
be studied with special care. Where it is possible to make the 
strength of the structure ample by correctly forming parts ex- 
posed to stress, as by making them cylindrical, it is usually con- 
sidered best to do so ; but in many types of boiler this is im- 
practicable, and staying must be resorted to. Properly designed 
stayed surfaces should be made the strongest parts of the boiler. 
The fireboxes of locomotives and of other firebox boilers, in 
which stay-bolts are well distributed, the water-legs of many 
marine boilers, and other parts composed of flat surfaces sus- 
tained by stays and braces, are common illustrations of the 
method of resisting pressure. 

Where flat surfaces are secured against lateral pressure by 
stay-bolts, as is done in steam-boilers, these bolts may yield 
either by breaking across, or by shearing the threads of the 
screw in the bolt or in the sheet. Such bolts should not be so 
proportioned that they are equally liable to break by either 
method, but should be given a large factor of safety (15 to 20) 
to allow for reduction of size by corrosion, from which kind of 
deterioration they are liable to suffer seriously. Wrought-iron 



MATERIALS— STRENGTH OF THE STRUCTURE. I45 

and soft steels are used for these bolts. They are screwed 
through the plate, and the projecting ends are usually headed 
like rivets. Nuts are sometimes screwed on them instead of 
riveting them when they are not liable to injury by flame. 

'' Button-set " heads are from 25 to 35 stronger than the 
conical hammered head, and nuts give still greater strength. 

Experiments made by Chief Engineers Sprague and Tower, 
for the U. S. Navy Department, lead to the following formula* 
and values of the coefficient a, p being the safe working pres- 
sure, t the thickness of plate, and d the distance from bolt to 
bolt: 

f 
P^a-j-,. . (i) 



Values of a in British and Metric Measures. 

A. Am- 

For iron plates and bolts 24.000 i,6g3 

For steel plates and iron bolts 25,000 1,758 

For steel plates and steel bolts 28,000 i,g68 

For iron plates and iron bolts with nuts 40,000 2,812 

For copper plates and iron bolts 14,500 1,020 

The working load is given in pounds on the square inch and 
kilogrammes per square centimetre, the measurements being 
taken in inches and centimetres. The heads, where riveted, 
are assumed to be made of the button shape. 

The diameter of stay is made, about 2 ^t, the number of 
threads per inch 12, or 14 (5 or 6 per centimetre). A very high 
factor of safety, as above, is recommended for stays, to afford 
ample margin for loss by corrosion. 

Lloyd's Rule for stayed plates is 

P = fy • . (2) 

in which / is the working pressure in pounds on the square 
inch, t^ the thickness of plate in sixteenths of an inch, and/, is 
the distance apart of the stays in inches. 

* Report on Boiler Bracing. Washington, 1879. 
10 



146 THE STEAM-BOILER. 

The coefficient a has the following value : 

« -^ 90 for plate -^-^ inch thick or less ; with screw stays 

and riveted heads ; 
^ = 100 for plate --^^ inch thick or more ; screw stays 

and riveted heads ; 
<2; = no for plate y^ inch thick or less ; screw stays and 

nuts ; 
a ^ \20 for plate y^g- inch thick or more ; screw stays and 

nuts ; 
a = 140 for plate -^ inch thick or more ; screw stays 

with double nuts ; 
a =^ 160 for plate y^-g- inch thick ; with screw stays double 

nuts and washers. 

The Board of Trade of Great Britain prescribes 



s-6 ' 



(3) 



in which t^ is the thickness of plate as above, and s is the area 
of surface supported, in square inches. 

a = 100 for plates not exposed to heat, and fitted with 
nuts and washers of 3'^ diameter and of f the 
thickness of the plates; 

^ = 90 for same case, but with nuts only ; 

^ ^ 60 in steam and having nuts and washers ; 

a = 54 if with nuts only ; 

a = 80 in water spaces, with screw stays and nuts; 

a = 60 ii with screw stays riveted ; 

<3; = 36 in steam, screw stays, riveted. 



For girder stays, 






where the symbols are defined as on page 148. When one, 



MATERIALS— STRENGTH OF THE STRUCTURE. I47 

two or three, or four bolts carry the girder, a = 500, 750, and 
800, respectively. 

Stay-bolts should have diameters considerably exceeding 
double the thickness of the plate. 

D. K. Clark allows, as a maximum, the pressure 



/ = 407^-, (5) 



where t, T, and d are the thickness of sheet and its tenacity, 
and the " pitch " of the stays in inches. 

In computing the strength of stayed surfaces, it is to be un- 
derstood that each stay sustains the pressure on an area bounded 
by lines drawn midway between it and its neighbors, and mea- 
sured by the product of the distances between stays in the two 
directions of the hnes of their attachments to the sheet. Thus 
marine boiler stays spaced 8 inches apart sustain the pressure 
on 64 square inches ; while locomotive firebox stay-bolts spaced 
4J inches each way carry the pressure on 20j square inches. 

A common minimum factor of safety for stays, stay-bolts, 
and braces is 8, and when liable to serious corrosion the load 
applied is often reduced to 3000 or 4000 pounds per square 
inch of section of stay or brace, thus giving a factor of ten or 
more. The actual rupture of stay-bolted surfaces was found by 
the Author, by the study of the results of experimental steam- 
boiler explosions in 1871,^ to be about the pressure 

P=[i^i2)' ■ (6) 

in which t is the thickness of plate, and d the pitch of the stay- 
bolts. In design, we would make 



365/ 

Va/ 



(7) 



Journal Franklin Institute, 1872. 



148 THE STEAM-BOILER. 

a being the factor of safety, which, as has been seen, should al- 
ways be large, and p' the working pressure. 

Fairbairn showed that the diameter of a stay-bolt should 
exceed double the thickness of the sheet by the amount to be 
allowed for corrosion. He found that riveting over the ends 
of screwed stays increased the strength of the construction 14 
per cent. 

Where the crown-sheet of the furnace of a boiler is supported 
by girders, the load to be permitted may be adjusted by the 
formula, already given, 

cdH 
P = 



{w-p')d'r 



in which 



w = width of the fire-box ; 

p' = the pitch of the supporting bolts ; 

d^ — the distance from centre to centre of girders ; 

/ = their length ; 

d = their depth ; 

t =^ their thickness ; 

all dimensions in inches except /, which is taken in feet. This 
is the formula approved by the British Board of Trade. The 
value of the coefificient c is from 500, when but one supporting 
bolt is used, to 750 and 800 when two or three and when four 
bolts are employed. 

The accompanying figure exhibits a common form of stay 
for water-legs and other narrow water spaces. 
The stay is cut from a long screwed rod, and 
is frequently fitted with a nut and washer at 
each end. They are sometimes drilled longi- 
tudinally in order that they may give warning 
by leakage if fractured. 

58. The Relative Strength of Shell and 

Fig. 68. << Sectlonal " Boilers, and consequently, in 

large degree, their relative safety, " is measured by the relative 

magnitude of their largest parts. As remarked by John Stevens, 




MATERIALS— STREXGTH OF THE STRUCTURE. 1 49 

the inventor, the sectional boiler, with its smaller members and 
subdivided steam and water chambers, is safe in proportion as 
the sizes of the latter are diminished ; while the large shells of 
the common forms of boiler are liable to dangerous rupture in 
proportion as their diameters are increased. The strengths of 
cylindrical reservoirs subjected to internal pressure, as are the 
shells, steam-drums, and mud-drums of shell boilers, and the 
tubes and steam-reservoirs of sectional boilers, are subject to 
laws so simple, and are computed by methods of such easy ap- 
plication, that there never need be any doubt in regard to the 
margin of safety existing in either case when new. Flues and 
old boiler-shells are less amenable to calculation, and are thus 
more unsafe. Water-tubular boilers are comparatively safe 
under all conditions of ordinary operation, and, when compared 
with the other type of steam-generator, are vastly safer. 

59. A Loss of Strength and of Ductility is very often ob- 
served in the iron of which boilers are composed, as they ad- 
vance in age, due to the progress of oxidation, probably, within 
and between the laminae of which the sheets may be composed. 
The plate may be thus very nearly destroyed, at times, before 
this action may be detected. In some cases the iron may be 
nearly all destroyed, and only a sheet of oxide may remain ; 
while the boiler, if not working under high pressure, may still 
appear sound. Such deterioration is often a source of great 
danger. 

Excessively high temperature hot infrequently gives rise to 
a loss of tenacity of serious amount with, fortunately, in most 
cases, increase of ductility. This is not invariably the case, 
however, as, at a " black heat " just below redness, a critical 
temperature is reached at which the iron may exhibit great 
brittleness. 

The physical conditions thus modifying strength have been 
already described at considerable length. These changes occur 
in steam-boilers through the action of a variety of special 
causes. Ordinary oxidation, general and local, especially when 
accelerated by voltaic action, produces in many cases rapid de- 
terioration ; the constant and often great changes of tempera- 
ture due to not only the ordinary working of the boiler, but also 



ISO THE STEAM-BOILER. 

at times to overheating of parts exposed to flame, may produce 
still more formidable effects ; and even the continual changing 
of form caused by variations both of pressure and temperature, 
after the lapse of considerable periods of time, may give rise to 
important losses of ductility, and sometimes of strength. Steel 
is especially liable, if too hard, to loss of quality and danger- 
ous injury by cracking, in consequence of such action. 

60. The Deterioration of Boilers with age and with use 
is in nearly all cases due to modification of quality of metal, 
and to reduction of section of parts exposed to stress and 
strain. This deterioration is certain to occur to a greater or 
less extent ; but its rate is usually indeterminate, and it conse- 
quently happens that, except by actual inspection and test, it 
is impossible to know, at any time after a boiler is built and 
set in operation, just what is its strength and whether it is safe. 

This deterioration may be to a certain extent controlled 
and retarded by care and by the adoption of proper precau- 
tions. The principal requisite is the keeping of every part dry, 
and at a temperature below that of " burning" or rapid oxi- 
dation. Loss of strength, elasticity, ductility, and resilience 
will, however, always take place ; and the boiler, whether in use 
or not, should always be very carefully examined at such inter- 
vals as shall insure its condition being known at all times, and 
such as shall secure a safe adjustment of the pressure main- 
tained within it to its reduced strength. Every element and 
member of the structure will inevitably depreciate, and the 
most insignificant part must be kept under proper supervision 
to insure safe operation. 

Experiment has shown that steel boiler-plate, exposed to 
repeated heating to high temperatures, and cooling down again,, 
loses less by oxidation than does iron,* and retains its quality 
better. Steel loses rather more than iron when exposed to the 
action of sea-water,f and should never, if it can be conveniently 
avoided, be placed under such circumstances in contact with 
iron. Its own scale also produces an acceleration of galvanic 



* Eiigineering , April 20, 1883. 

•}- Trans. Inst. Naval Architects, vol. xxiii. p. 143. 



MATERIALS— STRENGTH OF THE STRUCTURE. 15I 

action, and it is best, where practicable, to remove all the scale 
by '' pickhng" in dilute hydrochloric acid or in sal ammoniac. 

61. Inspection and Test of boilers, at regular intervals and 
by methods that are thoroughly reliable, is now universally rec- 
ognized as not only essential to permanent safe use of steam- 
generators, but also as necessary to secure maximum efficiency 
in their operation. 

Such examinations and tests are usually made by expert in- 
spectors who make a business of that work, and who have thus 
acquired exceptional, sometimes most extraordinary, skill in the 
detection of injury and its cause. The methods pursued and 
the rules adopted will be given later, in chapters devoted to 
the description of the methods of construction and to the pre- 
scription of forms of specification and contracts, and of the re- 
quisites of full conformance with the latter. 



CHAPTER III. 

THE FUELS AND THEIR COMBUSTION. 

62. The Chemical and Physical Principles involved in 
the combustion of fuel, the development of heat and its trans- 
fer, are all well known and capable of very definite expression. 

Combustion may be defined as the rapid combination of any 
oxidizable substance with oxygen. The result of such combi- 
nation is the production of new compounds of definite charac- 
ter, and in quantities readily calculable when the amount of 
each of the combustible constituents is given. It is also known, 
very precisely, how much heat is produced by the combustion 
of any given weight of any one of the more familiar combusti- 
bles, and how much of that heat is available for transfer to a 
steam-boiler or other apparatus of utilization, when the com- 
bustion is complete and perfect. 

Perfect combustion occurs when all of the combustible is 
burned, and with the result of producing the highest stage of 
oxidation. Carbon is perfectly burned when it is wholly con- 
verted into carbon dioxide and carbonic acid. Wood, or other 
fuel containing hydrogen, is perfectly consumed when all its 
carbon is oxidized to carbonic acid, and all its hydrogen is 
united with oxygen to form steam. 

Chemical combination invariably produces heat, and de- 
composition as inevitably results in the absorption of heat in 
precisely the amount due to the opposite process. If both 
combination and decomposition take place in complex chemi- 
cal changes, the heat produced is the net result of both actions. 

Several interesting and important principles are recognized 
by writers on this general subject, as controlling the develop- 
ment of heat by combustion. Berthelot first called attention 
to the fact that the total heat evolved in any case of chemical 



THE FUELS AND THEIR COMBUSTION. 153 

combustion is a measure of the energy expended in the separa- 
tion of the resulting compound into its elements. The same 
chemist announced a second law, also known by his name: 
The quantity of heat-energy evolved or absorbed in any chemi- 
cal change of this kind, where no mechanical work is done, is 
dependent purely on the initial and final states, and not at all 
on the intermediate process of change. Thus the heat pro- 
duced in a furnace depends on the final product of combustion, 
and not at all on whether the carbon, for example, has been, 
at intermediate stages, wholly or partly burned, and has existed 
in greater or less proportion in the state of carbon monoxide 
or of carbon dioxide. Berthelot's third law asserts that in any 
chemical action the tendency 'is toward that method of change 
which will yield the greatest amount of heat. In other words, 
the tendency always exists to produce complete transformation 
of potential into actual energy. 

63. The Fuels used in Engineering* are anthracite and 
bituminous coals, coke, wood, charcoal, peat, and combustible 
gases obtained by the distillation of the solid kinds of fuel. The 
oils — animal, vegetable, and mineral — and the solid hydrocar- 
bons, of which bitumen is a type, are occasionally used also. 
All consist of either pure carbon or of combinations of carbon, 
hydrogen, and non-combustible substances. The mineral oils 
and liquid fuels generally promise excellent results when satis- 
factory methods shall have been found to secure the conditions 
of perfect combustion. In making a selection of a fuel the 
engineer is aided greatly by a knowledge of the origin and 
general characteristics of those combustibles from which he 
may be called upon to select the one best adapted to any given 
case. 

Each form of fuel, solid, liquid, and gaseous, is specially 
adapted to particular purposes ; and in selection the engineer 
and . metallurgist should carefully examine all of the circum- 
stances of the case under consideration, in order to determine 
from which of these classes the fuel required should be selected ; 

* Adapted largely from the Author's "The Materials of Engineering," vol. i. 
N. Y. : J. Wiley & Sons, 1885. 



154 



THE STEAM-BOILER. 



and, this choice having been made, he will next select that 
quality which best fulfils the requirements of the case. 

COMPOSITION OF COMBUSTIBLES, CARBON TAKEN AS 100. 





Carbon. 


Hydrogen. 


Oxygen. 


Wood 


I GO 
lOO 
lOO 
lOO 
lOO 


12.48 

9-85 
8.37 
6.12 
2.84 


83.07 
55.67 
42.42 
21.23 
1.74 


Peat 


Lisrnite . 


Bituminous Coal 


Anthracite Coal 





Coal, whether anthracite or bituminous, is a fossil of vege- 
table origin. It is always associated with some earthy matter, 
and the latter is sometimes present in such quantities as to 
destroy the value of the coal as a fuel. 

Coal is sometimes found so slightly altered as to differ but 
little in chemical composition and in physical structure from 
recent vegetable substances ; and in other cases it is so 
thoroughly changed as to have become, in all but its chemical 
constitution, a mineral. Some of the more completely fossilized 
bituminous coal breaks into cubic and rhomboidal fragments, 
but the anthracite exhibits little or no traces of crystallization. 

Chemical examination shows coal, as already indicated, to 
be composed of both organic and inorganic matter. The for- 
mer is purely vegetable, and the latter consists of earthy mat- 
ter above which the ligneous portions once grew. 

Destructive distillation resolves the organic matter into its 
invariable ultimate constituents, carbon, hydrogen, and oxygen, 
which come from the retort as solid carbon, or coke, liquid tar, 
gaseous ammonia, benzole, naphtha, paraffine, illuminating gas, 
sulphurous acid, and other substances, in various proportions. 
The inorganic portion is left as an ash when the fuel is burned. 
It consists usually of silicates in varying proportions. 

The various fossil fuels having had a common origin, and 
being all more or less decomposed and mechanically altered 
vegetable matter, are found to exist in all states intermediate 
between that of recent vegetation and that of completely 
mineralized graphitic anthracite. 



THE FUELS AND THEIR COMBUSTION. 



155 



Their classification is therefore an arbitrary one, and it fre- 
quently happens that a particular species of coal lies so exactly 
between two classes as to make it difficult to determine to 
which it should be assigned. 

The anthracites are found among the older carboniferous 
strata; the bituminous coals come from the secondary, and the 
softest and least altered varieties from the tertiary, formations. 

The following, representing approximately the gradual 
change of composition as fossilization affects the alteration of 
woody fibre, is given by Dr. Wagner : 



CHANGE OF COMPOSITION OF FOSSIL FUELS. 





Carbon. 


Hydrogen. 


Oxygen. 


Cellulose 


52.65 
60.44 
66.96 
74.20 
76.18 
90.50 
92.85 


5-25 
5-96 
5-27 
5-89 
5.64 
5-05 
3-96 


42. ro 


Peat 


33-60 
27.76 
19.90 
18.07 


Lignite 


(earthy brown coal) 

Coal (secondary) 




4.40 
3-19 


Anthracite 





In the above analyses earthy matter is excluded. 

64. Anthracite Coal, called sometimes^/<3:/?^^, and sometimes 
blind or stone coal, consists of carbon and inorganic substances, 
and is usually free from hydrocarbons. Some varieties are 
thoroughly mineralized and have become graphitic. The or- 
dinary varieties of good anthracite are hard, compact, lustrous, 
and sometimes iridescent. The color is intermediate between 
jet black and that of plumbago. 

It is amorphous and somewhat vitreous in structure, the 
hardest varieties falling to pieces when suddenly heated, and 
sometimes breaking up into very small fragments, thus caus- 
ing considerable loss even when carefully "fired." It some- 
times gives out a ringing sound when struck. It is a strong, 
dense coal, its specific gravity ranging from 1.4 to 1.6. It has a 
high colorific value. 

It burns without smoke and without flame unless containing 
moisture, the vapor of which produces a yellow flame of com- 
paratively low temperature. It kindles slowly and with dif- 



156 THE STEAM-BOILER. 

ficulty ; and, once kindled, requires to be carefully and skilfully 
managed to secure economic efficiency. 

A representative variety has a specific gravity 1.55, and con- 
tains, exclusive of ash, carbon, 94 per cent, hydrogen and oxygen 
(moisture) 6 per cent. Of the latter, 2\ per cent is hygroscopic, 
but is held with great tenacity. 

The percentage of ash varies greatly, even in the same variety, 
and in specimens from the same bed. It may be estimated, as 
an average, at above ten per cent, while the total loss in ash, 
fine coal, and clinker will be likely sometimes to reach double 
that proportion in ordinary furnaces. When selecting anthracite 
it is necessary to keep this fact carefully in mind. Twenty-four 
samples of anthracite from Pennsylvania, analyzed by Britton, 
gave as a mean — 

Carbon , 91.05 

Volatile matter 3.45 

Moisture 1,34 

Ash o 4 16 

100.00 

There was included in the above, sulphur 0.240, phosphorus 
0.013. 

A variety of this class of coals, similar in composition, but 
differing from the typical anthracite above described in struc- 
ture, has been sometimes called semi-anthracite. 

It does not exhibit the conchoidal fracture of the latter, but 
is somewhat lamellar, and is marked by fine joints or planes of 
cleavage. It crumbles readily, and has less density than the 
preceding. ^ 

One method of distinguishing good examples of the two 
varieties is found in the fact that the latter, when just fractured, 
soils the hand, while the former does not. The latter variety 
kindles quite readily and burns freely. 

An example of this coal contained, in one hundred parts, 
carbon, 90; hydrogen and oxygen, 1.5; ash, 8.5. 

65. The Bituminous Coals are sometimes divided into 
three classes. 

Dry bituminous coal contains about 75 per cent of carbon, 



THE FUELS AND THEIR COMBUSTION. 1 57 

5 per cent hydrogen, and 4 per cent oxygen. That part of the 
hydrogen which is combined with carbon is capable of adding 
to the heat-giving power of the coal. This coal is lighter than 
anthracite, its specific gravity being about 1.3. Its color is 
black or nearly black, and its lustre resinous ; it is moderately 
hard, and burns freely. Its structure is weak, brittle and splin- 
tery, fine-grained, and of uneven surface. It kindles with less 
difficulty than any variety of anthracite, but less readily than 
the bituminous coal to be described. It burns with a moderate 
flame, and gives off little or no smoke. 

Bituminous caking coal contains sometimes as little as 60 per 
cent of free carbon, and the maximum proportion is, perhaps, 
70 per cent. It contains 5 or 6 per cent each of oxygen and 
hydrogen, and the remaining portion, amounting sometimes to 
30 per cent, is incombustible. Its specific gravity is about 1.25. 
It is moderately compact ; its fracture is uneven, but not splin- 
tery ; its color is a less decided black than the preceding, and 
its lustre is more resinous. When heated it breaks into small 
fragments if the proportion of bitumen is insufficient to cause it 
to cohere before becoming thoroughly softened, but afterward, 
as it becomes more highly heated, the pieces become pasty and 
adherent, and the whole mass becomes compact and hard as the 
gaseous constituents are expelled by heat. 

This coal, ignited in air, burns with a yellowish flame and 
very irregularly unless kept continually stirred to prevent ag- 
glomeration and consequent checking of the draught. It can- 
not be successfully used, therefore, when great heat is required. 
It is valuable for the manufacturer of gas and of coke, and can 
be used in small grates where but moderate heat is obtained. 

Long flaming bituminous coal is quite similar to the pre- 
ceding, differing chemically in composition and containing a 
larger proportion of oxygen. It burns with a long flame, and has 
a strong tendency to produce smoke. Some varieties cake like 
the preceding, others do not ; but all ignite readily and burn 
freely, consuming rapidly. 

There are many varieties of coal in each of the above- 
named classes, the gradation being sometimes marked and 
sometimes barely distinguishable. 



153 THE STEAM-BOILER. 

American anthracites have been found, by experiments 
made under the direction of the United States Navy Depart- 
ment, to have a mean evaporative efficiency, in marine boilers, 
of 8.9 pounds of water evaporated from 212° Fahr. (100° Cent.) 
per pound of coah The bituminous coals of the United States 
were found to evaporate an average of 9.9 pounds of water per 
pound of fuel, under similar conditions. The average efficiency 
of British coals is given by Bourne at about 8.7. American 
anthracites evaporated 10.69 pounds of water per pound of 
combustible matter contained in the fuels, and the bituminous 
coals 10.84, from 212° Fahr."^ 

These results are practically identical for the two kinds of 
coal ; but the average of the best known varieties gives a dif- 
ference which is, with such good varieties, in favor of anthra- 
cite. 

66. Lignite, or Brown Coal, is of more recent and of more in- 
complete formation than the bituminous coals, and occupies a 
position intermediate between the true coals and peat. It con- 
tains from 30 to 60 per cent of carbon, 5 to 8 per cent of 
hydrogen, and 20 to 25 per cent of oxygen. It is very light 
when pure, having, according to Regnault, a specific gravity of 
from 1. 10 to 1.25. The heavier varieties contain much compact 
earthy matter. 

Lignite is found in tertiary geological formations. It is 
brown in color, has the woody structure well defined, and is 
usually lustreless. Where it approaches the bituminous coals 
in age, it also approximates to them in structure and other 
characteristics. It frequently contains considerable moisture, 
which can only be removed by high temperature or by long 
seasoning, and the lignite, once dried, must be carefully pre- 
served in dry situations if not used at once, as it reabsorbs 
moisture with great avidity. 

When thoroughly dry it kindles readily, burns freely, and 
is consumed rapidly. It is not usually considered a valuable 
kind of fuel. It occupies considerably more space weight for 
weight than the true coals, burns as an average a third more 

* See American Institute Reports: Tests of Steam Boilers, 1874. 



THE FUELS AND THEIR COMBUSTION. 1 59 

rapidly, and its evaporation of water per pound of fuel is about 
25 per cent less. To obtain maximum evaporative efficiency a 
slow rate of combustion is found most effective. 

67. Peat, sometimes called Turf, is obtained from bogs and 
swampy places. It consists of the interlaced and slightly 
decayed roots of vegetation, which, although buried under a 
superincumbent mass of similar material and mingled with some 
earthy matter, retains its ligneous structure and nearly all 
the chemical characteristics of unaltered vegetable matter. 
Submitted to the great pressure and the warmth which have 
for ages acted upon the coal-beds, it would also probably 
become coal. 

Dried in the air, it, like the lignites, retains moisture per- 
sistently, and is usually found to contain 30 per cent after 
drying. After completely removing all water, an average 
specimen would contain about 60 per cent of carbon, 5 to 10 
per cent hydrogen, and 30 or 40 per cent of oxygen. The ash 
varies very greatly, sometimes being as little as 5, and in other 
cases as high as 25 per cent. 

A pound of wood charcoal has nearly the same value as a 
fuel as 1.66 pounds of peat of average quality. 

Peat is frequently used in large quantities for heating pur- 
poses, and attempts have been made, with encouraging results, 
to use it in metallurgical operations. 

When to be thus used, it is cut from the bog with sharp 
spades, ground up in a machine specially designed for the 
purpose, and dried by spreading it where it can have full 
exposure to the sun and air. 

It is frequently compressed by machinery until its density 
approaches that of the lighter coals, and it is used in blocks 
of such size as are found best suited to the particular purpose 
for which it is prepared. 

Its charcoal makes excellent fuel for use in working steel 
and welding iron. It is frequently found to be a very excel- 
lent fuel for other purposes, and is extensively used in some 
localities. Its specific gravity is usually about 0.5. 

68. Wood, thoroughly seasoned, still contains about 20 per 
cent of moisture. 



l6o THE STEAM-BOILER. 

The moisture being completely driven off by high tem- 
perature, there is left about 50 per cent carbon, and combined 
oxygen and hydrogen compose the remainder, in very nearly 
the proportions which form water. The pines and firs contain 
turpentine, and other woods contain frequently a minute pro- 
portion of hydrocarbons peculiar to themselves. 

The proportion of ash varies from about 0.5 per cent to 5 
per cent. The woods all evaporate very nearly the same weight 
of water per pound of fuel. The lighter woods take fire most 
readily and burn most rapidly ; the denser varieties ^\n^ the 
most steady heat and burn longest. 

Where radiated heat is desired the hard woods are much the 
most efficient. 

The seasoning of wood has been described in that part of 
this work which treats of timber. 

Thorough seasoning in the open air requires from six 
months to a year, and is the only method generally adopted 
for wood intended to be used as fuel. One cord of hard wood^ 
such as is used on the Northern lakes of the United States, is 
said to be equal in calorific power to one ton of anthracite coal 
of medium quality. One cord of soft wood, such as is used by 
steamers on Western rivers, is equal in heating power to 960 
pounds (436 kilogrammes) or 12 bushels (423 cubic decimetres) 
of Pittsburg coal. One cord of well-seasoned yellow pine is 
equivalent to \ ton (500 kilogrammes) of good coal. (See § 84.) 

69. Coke is made from bituminous coal by subjecting it to 
such high temperature as to deprive it of its volatile con- 
stituents. 

The presence of moisture in some of the coals largely 
reduces their heating power. The bituminous matter causes 
them to fuse and to form a coherent mass, and, by thus pre- 
venting the passage of air, destroys their efficiency for many 
purposes. The presence of sulphur and of deleterious volatile 
substances in many coals also precludes their application to the 
reduction of iron ores, and destroys their value for other metal- 
lurgical purposes. All of these volatile materials being driven 
off by heat, a mass of fixed carbon containing only earthy 
impurities remains, which " coke " constitutes the fuel with 



THE FUELS AND THEIR COMBUSTION. l6l 

which some of the most extensive and important metallurgical 
industries are conducted. These volatile matters are sometimes 
utilized, but are generally wasted, except where the coke is 
considered a secondary product, as in the manufacture of illu- 
minating gas. 

Coking is carried on by either of three methods — in open 
heaps, in coke ovens, or in retorts. 

The first method is extremely wasteful, and is rarely prac- 
tised ; the second is more economical ; and the third is the best 
where gas is manufactured, and is the only one practised in 
that case. The second method is that generally adopted where 
the coke is the primary product, as, although not as economical 
as the last, it produces a strong coke which is much better 
adapted for use in furnaces than that afforded by the last 
method, which, although allowing of the complete separation 
and collection of the liquid and gaseous products of distillation, 
yields a coke which has too little density and strength to make 
it a valuable fuel. 

Coak made in ovens is usually of a dark gray color, porous,, 
hard, and brittle. The best gives out a slight ringing sound 
when struck, and has something of the metallic lustre. It 
makes an intense, clear fire, and it should not be forced so as 
to injure either the boiler or the grate by burning the iron. 
Where the coals contain sulphur but are free from moisture, 
provision should be made for the passage of a supply of steam 
through the oven. This will give up its oxygen to the metal 
with which the sulphur is combined, and the hydrogen, uniting 
with the latter, forms sulphuretted hydrogen. The coke is 
thus left comparatively free from the noxious ingredient, and 
as this is usually the only constituent of bituminous coal which 
injuriously affects iron, the coke is a better fuel than the coaL 
from which it is made. 

Various coals yield from 33 per cent to 90 per cent of their 
weight in coke. The latter containing all the ash, the percent- 
age of ash in coke will be higher than in the coal from which it is 
prepared. Coke has a strong tendency to absorb moisture, and 
may, when unprotected from dampness, condense 15 or 20 per 
cent of its own weight within its pores. 



1 62 THE STEAM-BOILER. 

Many cokes contain 15 percent ash and i or even 2 per 
cent sulphur ; while others contain but 3 to 5 per cent ash and 
Jq- per cent sulphur. 

70. Charcoal has the same relation to wood that coke has 
to bituminous coals. 

It is made from all kinds of wood, hard-wood charcoal 
being the best for fuel. Wood of about twenty years of age is 
preferred, and should be charred before decay has commenced. 
The methods of preparation are substantially the same, and the 
chemical constitution of the product is very similar, although 
its physical characteristics are quite different. 

Charcoal prepared by charring in heaps seldom amounts to 
more than 20 per cent of the total weight of wood used ; care- 
lessness in conducting the process may reduce the weight of 
product far below even that figure. A considerable loss is 
unavoidable, since the charring of one portion must be effected 
by the heat obtained from the combustion of another part of 
the wood. Sound wood is selected, cut in billets four or five 
feet in length, and, when large, split into sticks of from three 
to six inches in thickness. It is best to assort the wood, 
placing each kind in piles by itself. In making up the heap 
the ground is cleared, a stake is set at the centre of the cleared 
space, and a layer of wood is put down with all the sticks laid 
radially, and the interstices filled with smaller sticks. On this 
layer the rest of the wood is piled on end, beginning by leaning 
sticks against the centre stake. The whole is finally covered 
with another closely packed layer, which in turn is completely 
covered with sods. 

A central hole is left, and also an uncovered ring around the 
base five or six inches high, for the air-supply. One or two 
horizontal passages left in the pile conduct the gases to the 
centre, where they rise, passing out at the hole made by pulling 
out the centre stake before firing the pile. 

The fire being started and actively burning, all openings 
are closed, and combustion is perfectly controlled by altering 
their number and position. The condition of the fire is indi- 
cated by the color of the smoke, which should be black and 
thick ; when it is light and bluish the draft should be more 



THE FUELS AND THEIR COMBUSTION. 1 63 

completely checked. The work is finished when the wood at 
the exterior of the pile is found charred. All openings are 
then closed, and the fire is thus extinguished. The pile can 
be .usually opened on the following day, and the removal of 
charcoal begun. So crude a process is very liable to excessive 
losses from the dif^culty experienced in adjusting the supply 
of air, and in conducting the heated products of combustion to 
precisely the right points, and in precisely the right proportions 
to secure maximum efficiency. 

The presence of moisture in wood is productive of loss 
by giving rise to the formation of carbonic oxide and of new 
hydrocarbons. They carry ofT carbon which would otherwise 
have been left in the solid state as so much charcoal. 

Dry wood, charred in a retort, yields as a maximum about 
30 per cent of its weight in charcoal. Of the carbon originally 
contained in wood, therefore, by the first method of charring 
not above one half may be expected to be obtained as charcoal, 
while by the last method three quarters may be obtained by 
skilful management. The latter process requires the expen- 
diture of about one eighth of the weight of wood charred for 
the production of the heat demanded by that process. It 
therefore yields a net amount in charcoal of about 30 per 
cent of the total weight of wood used. The wood which is 
used for fuel, however, may be of less value than that charged 
into the retort. Peat charcoal is sometimes made by similar 
methods, but is little used. 

Wood heated to 300° Fahr. (150° Cent.) for a considerable 
length of time loses 60 per cent or more of its weight. If 
heated only to slightly above 212° Fahr. (100 Cent.), the loss 
is but from 50 to 55 per cent. The residue resembles charcoal, 
but in each case it retains some volatile matter which may be 
driven off by higher temperatures. Karsten found that, by 
rapid charring at high temperatures, he obtained as an average 
about 15 per cent charcoal in one series of experiments; while 
by slowly charring the same woods at a low temperature the 
percentage obtained averaged about 25 per cent. 

The combustibility of charcoal is greater when prepared at a 
low than when prepared at a high temperature. 



164 THE STEAM-BOILER. 

Good charcoal is black, with a high lustre, and has a con- 
choidal fracture. It is quite strong, and the best qualities ring 
when struck, although less than good coke. It burns without 
flame or smoke, and radiates heat strongly. It should not soil 
the hands. 

Charcoal and coke both make an intense, clear fire, and with 
a forced draught, giving a small air-supply, afford an extremely 
high temperature, which is liable to injure the grates or anything 
metallic which may be subjected to its action. 

71. Pulverized Fuel, or Dust-fuel, is sometimes used in 
special processes. In the use of this form of fuel special ar- 
rangements become necessary to secure thorough intermixture 
of the fuel with the supporter of combustion, in order to effect 
complete oxidation. The fuel itself is sometimes prepared by 
pulverizing coal or other combustibles; and sometimes it is 
obtained from the large deposits of ''slack," "breeze," or coal 
dust which are found wherever coal in large quantities is sub- 
jected to attrition. It is sometimes burned on a very fine grate, 
the requisite supply of air being secured by the use of a blast 
beneath the grate. 

One of the most successful methods is that pursued by 
Whelpley and Storer, and by Crampton. In this process a 
stream of mingled dust-fuel and air is driven into the furnace 
where combustion takes place, the quantity of fuel and of air 
being capable of adjustment in such a manner as to secure the 
most perfect combustion. This method has been applied suc- 
cessfully, not only in the production of heat simply, but also in 
the reduction of metals from their ores. The facility with 
which an oxidizing or a reducing flame may be produced at 
will is the great merit of the process in the latter application. 
Its advantage for heating purposes lies in the power which it 
gives of utilizing a fuel which would have otherwise no value. 
In making " muck-bar," an economy over that attained with 
coal of above 20 per cent has been reported to have been 
effected by the use of this process and fuel. The saving 
occurred in reduction of waste of metal, as well as in simple 
economy of fuel. At the United States Armory at Springfield, 
Massachusetts, 6.6 pounds or kilogrammes of fuel were con- 



IHE FUELS AND THEIR COMBUSTION l6$ 

sumed per pound or kilogramme of iron heated to the welding 
heat, where i6 had been required by the old process.* 

72. Liquid Fuels have been used to a limited extent. The 
liquids best adapted for use as fuel are the mineral oils. They 
yield an intense heat ; the products of combustion, as well as 
the fuels themselves, are comparatively free from deleterious 
elements, and the temperatures obtained by their use are 
generally easily regulated, when they are burned in manageable 
quantities. Their tendency is to give off combustible gases, 
which may cause serious explosions ; and this fact, but especially 
the difficulty met with in uniformly distributing the oil, and in 
properly supplying it with air for its combustion, have hitherto 
prevented the general use of these fuels, even where their com- 
paratively high cost would not be a serious objection to their 
application. 

Crude petroleum, on distillation, breaks up into a large 
number of hydrocarbon compounds, having boiling-points 
varying from 32° Fahr. (0° Cent.) to 700° Fahr. (371° Cent.), as 
given by Van der Weyde. Its density is variable, but usually 
about 45° Beaume, corresponding to a specific gravity of about 
0.8, the gallon weighing 6.67 pounds, and the litre weighing 0.8 
kilogramme. It contains by analysis : carbon, 84 ; hydrogen, 
14; oxygen, 2. The latent heat of its vapor is about one fifth 
that of steam, and its volume 25 cubic feet to the gallon of oil, 
or 0.2 cubic metre per litre. 

The " creosote" or "dead oil" produced in gas-making is 
sometimes used as fuel. In experiments on board the British 
steamer Retriever , in 1868, where creosote was used for the 
generation of steam by what is called the Dorsett system, the 
evaporation was about 14 pounds or kilogrammes of water 
from a boiling-point per pound or kilogramme of liquid fuel 
used, or nearly double the average obtained where coal was used 
in the same boiler. 

Dr. Paul, reporting these results, gives the theoretic evapo- 
rative power of the constituents of this fuel, in units in weight 
of water per unit of fuel, as follows: phenol, 12.25; cressol, 

* Report, Lieut. H. Metcalf to Major Burton, Oct. 31st, 1873. 



1 66 THE STEAM-BOILER. 

13.01; napthaline, 15.46; xylol, 16.59; cumol, 16.78; cymol, 
16.94. 

Capt. Selvvyn, R. N., reported an evaporative power from 
boiling-point of 16.77 parts water per part by weight of a 
liquid fuel which had a theoretical efficiency of 17.52 parts. 
In another instance he gives the evaporation of 14.98 from 
the boiling-point, by a fuel having a theoretical evaporative 
power of 17.5. Deville found oil from Oil Creek, Pennsylva- 
nia, to have a calorific value of 10,000 "calories," equivalent to 
the evaporation of 16.17 parts of water for one part by weight 
of oil. Of this 13^ per cent was lost by the chimney, and by 
conduction and radiation. Some other oils give slightly higher 
figures. 

Liquid fuels have probably had most general and success- 
ful application in Russia, where Mr. Urquehart and others 
have adopted it for locomotives, and many steamers in South- 
ern Russia have been fitted with petroleum furnaces. In these 
cases crude petroleum and refuse is injected into the furnace 
by means of a steam-jet in which highly-superheated steam is 
employed. The furnace is lined with fire-brick and the com- 
bustion-chamber as well, the burning jets passing first through 
the latter, then onward to the furnace, where combustion is 
completed. The brickwork serves as a reservoir of heat, regu- 
lating the supply, and also at times re-igniting the jets of oil- 
spray when they have been for a short time extinguished. 

The use of oil on the steamers of the Central Pacific Rail- 
way Co. gave in 1884 an economy of from 5 to 12 per cent in 
total running expense as compared with coal, with great saving 
of boilers also. 

Experiments made by Engineer-in-Chief B. F. Isherwood, 
U. S. N., under the direction of the U. S. Navy Department, 
upon various systems of utilization of petroleum as a fuel, 
gave a maximum economy over the use of anthracite of 68 
per cent by Fisher's method of burning oil, and 38 per cent 
by Foote's process of burning liquid and solid fuel together ; 
he reports the failure of another method, in consequence of 
the obstruction of the tubes by deposition of solid carbon. 

Isherwood states the advantages attending the use of the 



THE FUELS AND THEIR COMBUSTION. 1 67 

mineral oils, which were the subject of his experiments, as fol- 
lows : 

1. A reduction of weight of fuel amounting to 40^- per cent. 

2. A reduction in bulk of 36J per cent. 

3. A reduction in the number of firemen ('' stokers") in the 
proportion of 4 to i. 

4. Prompt kindling of fires, and consequently the early 
attainment of the maximum temperature of furnaces. 

5. The fire can at any moment be instantaneously extin- 
guished. 

Other advantages, unmentioned by him, are the uniformity 
of combustion and heating attainable, and the small propor- 
tion of ash. The disadvantages are given as follows : 

1. Danger of explosions occurring by the taking fire of 
the vapors which are liable to arise from the fuel, and to 
escape from the tanks. 

2. Loss of fuel by evaporation. 

3. The unpleasant odors which distinguish these vapors. 

4. The comparatively high price, which price would be 
rapidly augmented by any general introduction of the pro- 
posed application of the oils.^ 

73. Gaseous Fuels are used with marked success in some 
branches of metallurgical work, as well as in the generation of 
heat for ordinary purposes. 

The advantages possessed by gaseous fuels are : 

1. Convenience of management of temperature. 

2. Freedom from liability to injure material with which 
the products of combustion may come in contact, and conse- 
quently, also, allowing the use of fuel of inferior quality as a 
source of the gas. 

3. The facility with which thorough combustion may be 
secured. 

4. The readiness with which the flame may be given either 
an oxidizing or a deoxidizing character. 



* This may be questioned, since recent explorations of oil deposits, especially 
of the United States, indicate an immense supply — as immeasurable and probably 
nearly as inexhaustible as the coal-fields. ' 



l68 THE STEAM-BOILER. 

5. In many cases economy in expense of operation. 
The disadvantages are : 

1. Danger of explosions when carelessly or unskilfully 
handled. 

2. Expense of plant. 

74. Artificial Fuels, other than charcoal, coke, and gases, 
are occasionally used in the production of high temperatures. 

They are prepared principally from refuse of natural fuels, 
which has but little value in its usual condition, but which, by 
special processes, is simply mixed with a small proportion of 
fuel of better quality or of more manageable form, and is 
compressed by machinery into conveniently shaped blocks, 
called briquettes. This refuse is found in large quantities in 
the neighborhood of coal-mines, and wherever coal is handled 
in considerable quantities. 

The total loss in this form in mining and transportation 
amounts to from one third to one half. It is called, as has 
been before stated, slack-coal. 

In the manufacture and transportation of coke and of 
charcoal, large quantities of refuse, called '* breeze," accumu- 
late ; which, although very rich in combustible matter, can- 
not be utilized in the condition in which it is found, except 
by special contrivances. The sawdust which accumulates 
about saw-mills is another variety of combustible belonging 
to the same class ; as is also spent tan-bark, from tanneries, 
and '' bagasse," or refuse crushed sugar-cane. 

They are most frequently mixed with some cohesive and at 
the same time combustible substance, as coal-tar. In districts 
abounding in mineral hydrocarbons, as in the neighborhood 
of the Caspian Sea, it has long been customary to mix them 
with clay, and thus to form a coherent and manageable fuel. 
The Norwegians have also long practised their method of 
utilizing sawdust • by mixing it with clay and vegetable tar, 
and moulding it into bricks of such size and shape as to be 
conveniently handled, and at the same time to burn freely 
and without waste. It has been often urged, and with some 
reason apparently, that for many purposes a fuel made by 
careful mixture of dust-fuel with pitch or other combustible 



THE FUELS AND THEIR COMBUSTION. 1 69 

cementing material is preferable to ordinary coal, in conse- 
quence of the greater convenience with which it can be stowed 
and handled. 

Another method of utilizing waste fuels consists in thor- 
oughly mixing, by grinding, charcoal-dust from the kilns with 
charred peat, spent tan-bark, and the proper proportion of tar 
or pitch to make a pasty, adhesive mass. This is moulded by 
machinery and dried in the open air, and then finally baked 
in closed retorts at a low heat. Dust-coal and pitch have been 
made into a good fuel in quite a similar manner to that just 
described. 

75. The Heating Power of any Fuel is determined by 
calculating its total heat of combustion. This quantity is the 
sum of the amounts of heat generated by the combustion of 
the unoxidized carbon and hydrogen contained in the fuel, less 
the heat required in the evaporation and volatilization of con- 
stituents which become gaseous at the temperature resulting 
from the combustion of the first-named elements. It is meas- 
ured in " thermal units." 

A thermal unit is the quantity of heat necessary to raise a 
unit weight of water, at temperature of maximum density, one 
degree of temperature. The British thermal unit is the quan- 
tity of heat required to raise a pound of water from the tem- 
perature 39°. I to 40°. I Fahr. The metric unit or calorie is the 
quantity of heat required to raise one kilogramme of water 
(2.2046215 pounds) from 3°.94 to 4°.94 Centigrade. 

One metric or centigrade unit is equal to 3.96832 British 
units, and a British unit is equal to 0.251996 metric unit. 

An approximate estimate of the number of thermal units 
developed by the combustion of a pound or kilogramme of any 
dry fuel, of which the chemical composition is known, may be 
obtained by the use of the following formula : 



h = 14,500c + 62,ooo\^H — —j, 
k' = 8,o8o(: + 34,462 [h - -?-) , 



(I) 



I/O THE STEAM-BOILER. 

where h is the number of British thermal units representing the 
total heat of combustion of one pound of the fuel ; // is the 
number of metric units per kilogramme of fuel ; C represents 
the percentage of carbon, H that of hydrogen, and O that of 
oxygen. 

Thus an anthracite coal has been found to have the follow- 
ing composition: 

COMPOSITION OF ANTHRACITE COAL. 

Per cent. 

Carbon 8 1 . 34 

Hydrogen, uncojiibined. 3-45 

Hydrogen, in co77ibination o. 74 

Oxygen and Nitrogen 5 . 89 

Sulphur 0.64 

Water , 2.00 

Ash 5 . 94 

Total 100.00 

One pound or kilogramme of coal, of which the above is an 
analysis, can evaporate theoretically 14.4 pounds or kilogrammes 
of water from and at 100° Centigrade, or 212° Fahr. 

M. M. Scheurer, Kestner, and Meunier have adopted the 
common formula as first proposed by Dulong, but would omit 
all account of oxygen, thus reducing, as is claimed, the average 
error of the formula from about 12 per cent or more to S 
or 10. M. Cornut would separate the fixed from the volatile 
carbon, and would give the latter about one third more credit 
for heating power than the former ; closer approximations are 
thus made than by the other methods. 

Various methods of approximate determination of the 
heating power of fuels have been proposed. The use of the 
calorimeter is probably the most satisfactory; another method 
is that of computation from the known chemical composition 
of the fuel, and the law of Walter, who found the quantity of 
heat produced in combustion very closely proportional to the 
weight of oxygen absorbed. Berthier's method is often em- 
ployed : this consists in heating the fuel sample to a red heat, 
in a closed vessel, with litharge or other source of oxygen. 
When lead oxide is thus used, the weight of lead reduced to 



THE FUELS AND THEIR COMBUSTION. I/I 

the metallic state is a measure of the oxygen absorbed. The 
method is simple and easy of practice, but is not sufficiently 
accurate to be generally approved. 

The value of h or of ^'ranges between 5500 British or 1386 
metric units for dry wood, and 16,000 or 4032 for the best 
known coals. The equation given is deduced from the experi- 
ments of MM. Favre and Silbermann, who determined the 
total heat of combustion of one pound of pure carbon to be 
14,500 British or 3654 metric thermal units, and of one pound of 
hydrogen to be 62,000 British units, or 15,624 calories. The 
combustion of one kilogramme of each would develop 31,967 
British or 8080 metric units, and 136,686 British or 34,462 
metric units, respectively. 

The combustion of the several kinds of carbon produces the 
development per unit of weight of : 

British Units. Metric Units. Material. 

13,986. . . 7,770 Diamond. 

13,968 7.760 Iron Graphite. 

14,040 7,800 Natural Graphite. 

14,490 ; . . .8,050 Gas Carbon. 

14,500 8,080 Wood Charcoal. 

Where the chemical composition of the fuel is unknown 
and cannot be readily ascertained, its heating effect may be 
determined experimentally by burning a known weight and 
passing the products of combustion through a calorimeter of 
such area of heating-surface as to reduce their temperature very 
nearly to that of the atmosphere before discharging them. 

The table given hereafter exhibits the total heating effect 
of various fuels as estimated from analyses of good specimens. 

Where the heat produced is not so thoroughly utilized as to 
cause the condensation of vapors which may pass off with the 
permanent gases resulting from combustion, there is necessarily 
a greater loss of the heat of combustion of hydrogen than of 
that of carbon, and the relative heating efficiency of carbon is 
considerably increased by the facts that it must be raised to 
red heat as a solid before combustion can occur, and that the 
specific heat of carbonic acid (0.216) is only about one half that 
of aqueous vapor (0.475). 



172 THE STEAM-BOILER. 

The general formulas, as given by Watts, for ascertaining 
the thermal effect of any fuel of a known composition are as 
follows : 

For combustion in oxygen : 



cC-^c'H-lW 



For combustion in air : 

cC-\-c'H-lW 



s.z.67C + 9H+s'W-\-s"N + s'"A' 



(3) 



Here 7"= increase of temperature produced by combus- 
tion ; 
^'and //"= quantities of carbon and hydrogen available in 
I part by weight of the fuel ; 
W =^ total quantity of water yielded by I part by 
weight of the fuel ; 
/ = latent heat of water ; 
J, s', s"j s'" = specific heat of carbonic acid, water-vapor, 
nitrogen, and air ; 
c and c' = calorific power of carbon and hydrogen ; 

iV= quantity of nitrogen in air necessary for con- 
verting combustible constituents of i part by 
weight of fuel into carbonic acid and water; 
A = extra quantity of air supplied for combustion. 

76. The Temperature of the Fire depends, not solely on 
the amount of heat generated by combustion, but also on the 
quantity and nature of the resulting products of combustion. 

The total heat generated by the combustion of fuel is all 
communicated to the products of combustion, which are usu- 
ally gaseous, giving them a temperature which is determined, 
partly by the calorific power of the fuel, and partly by their 
nature. Thus, carbon requires for its combustion to carbonic 



THE FUELS AND THEIR COMBUSTION. 1/3 

acid 2.67 times its weight of oxygen, producing 3.67 times its 
weight of carbonic acid. 

The heat generated by combustion of carbon is capable of 
raising 8080 times its weight of water from 4° to 5° C, and 
would raise the temperature of water equal in weight to the 
carbonic acid produced, about 2202° C."^ — i.e., 8080 X 1° = 
220i°.63 X 3-67- 

But the specific heat, or capacity for heat, of water is 
greater than that of carbonic acid ; the increase of temperature 
in the carbonic acid produced is correspondingly greater than 
the rise in temperature that would be produced in a quantity 
of water equal to 3.67 times the weight of carbon burnt. The 
quantities of heat necessary to produce equal increase of tem- 
perature in equal weights of carbonic acid and of water being 
in the proportion of 0.2164 : i.oooo, the amount of heat needed 
to raise the temperature of 3.67 parts water and 3.67 parts car- 
bonic acid one degree, are as 

3.67 3.67 



3.67 X 0.2164 0.794 

Hence the rise in temperature of the 3.67 parts of carbonic 
acid, to which the heat of combustion of i part carbon is trans- 
ferred, maybe calculated by dividing the given number of heat- 
units by the amount of heat required to raise the temperature 
of the 3.67 parts carbonic acid one degree, or 



^''^'' = 10,174- C. = 18,345° F. 



0.794 



The heat of combustion of hydrogen is sufificient to raise 
the temperature of 34,462 times its weight of water 4° to 5° 
Cent., but it requires for its combustion 8 times its weight of 
oxygen, and produces 9 times its weight of vapor. The prod- 

* Watts' Dictionary of Chemistry. 



174 THE STEAM-BOILER. 

ucts of combustion weigh nearly 2\ times as much as those of 
the combustion of an equal weight of carbon. Some of the 
heat produced by the combustion of hydrogen becomes latent 
and does not increase the temperature of the gases. 

The latent heat of water, or that needed to convert i part 
of water at ioo° C. into steam, is 537 times as much as is 
needed to raise the temperature of an equal weight of water 
from 4° to 5° C, and 966.1 times the quantity which will raise 
the temperature of one part from 39°.! to 40°.! Fahrenheit. 
The quantity of heat latent in the 9 parts vapor produced by 
the coinbustion of hydrogen will therefore be 4833 metric heat- 
units ; this must be taken from the total amount of heat gen- 
erated in calculating the quantity of heat producing rise in 
temperature. 

Parts by Metric British 

weight of Heat- Heat- 

water vapor, units. units. 

Total heat of combustion of i part 

hydrogen 34,462 62,000.0 

Latent heat of water in heat-units. . 9X 537= 4,833 9X966.1= 8,694.9 



Available heat 29,629 = 53,305.1 

The specific heat of water vapor is 0.475 i the heat raising 
the temperature of 9 parts water and 9 parts water vapor have 
the proportion 

9X1' _ 9 



9 X 0.475 4.275 
and the rise in temperature will be 
29629 



4.275 



= 6930^.7 C. = i2,475°.3 F. 



Thus the heating and the calorific power are not necessarily l| 
the same. The heating effect depends only partly upon the 
calorific power of the fuel burnt. 



THE FUELS AND THEIR COMBUSTION. 



175 



RECAPITULATION. (WATTS.) 



Carbon. . . . 
Hydrogen.. 



Weight. 


Weight of 
Oxygen. 


Ratio. 


Weight of 
Products. 


Ratio. 


Heat- 
units. 


Ratio. 


Thermal 
Effect. 


I 
I 


2.67 
8 


I 
3 


3.67 
9.00 


I 
2.4 


8080 
34,462 


I.OOO 
4-265 


10176° 
6930.7° 



Ratio 



I.OOO 
0.681 



In these examples combustion takes place in oxygen, and 
with no more than is theoretically needed. In all actual cases 
of combustion, atmospheric air supplies the oxygen supporting 
the combustion. Nitrogen, of which it contains 77 per cent, 
•dilutes the products of combustion and reduces the tempera- 
ture. In the case of combustion of carbon in air, the nitro- 
gen in air containing 2.67 parts of oxygen amounts to 8.94 by 
weight. 

The specific heat of nitrogen is 0.244, and the quantity of 
heat needed to raise the temperature of the nitrogen from 4° 
to 5° C. is: 

8.94 X 0.244 =2.181 units. 

Adding to this the heat needed to raise the temperature of 
the carbonic acid produced, the amount of heat needed to raise 
the temperature of all the products of combustion in air from 
4° to 5° C. will be 

2.181 -f 0.794 = 2.975 units. 
And the elevation of temperature will be 



8080 



2715° C. = 4887°F. 



Burning hydrogen in air, the nitrogen in air containing 8 
parts of oxygen is, by weight, 26.78 parts, and the amount of 
heat needed to raise its temperature from 4° to 5° C. is: 



26.78 X 0.244 = 6.534 units, 



176 THE STEAM-BOILER. 

and the consequent rise in temperature will be 



29629 



4.275+6.534 



= 2741° C. = 4934° F. 



The difference between the temperatures attainable by the 
combustion of carbon and hydrogen in oxygen and in air is 
much the greatest with carbon, as the quantity of heat pro- 
duced by its combustion is much less than that generated by 
burning hydrogen, thus : 



RECAPITULATION. (WATTS.) 





Calorific 
Power. 


Ratio . 


Temperature Produced. 


Dif- 
ference. 






In 
Oxygen. 


Ratio. 


In Air, 


Ratio. 


Ratio. 


Carbon 

Hydrogen 


8.080 
34-460 


I.OOO 
4-265 


10,174° 
6,930° 


I.OOO 

0.68] 


2.715° 
2,741° 


1.002 
1.009 


7,459 
4.189 


I.OOO- 

0.561 



Thus in all cases where high temperatures are demanded, it 
is of advantage to increase the amount of oxygen in the air 
supporting combustion, and to restrict the influx of nitrogen 
and of superfluous air. Thus also the reason of the attainment 
of high temperatures by combustion in pure oxygen with the 
oxyhydrogen blow-pipe is readily seen. 

The quantity of air supplied is usually much greater than 
that simply required to furnish the oxygen to consume the 
combustible. In practice it often amounts to twice as much, 
and is rarely less than one and a quarter times the quantity 
theoretically needed, and there consequently follows a propor- 
tionate reduction of the temperature attainable. When carbon 
is burnt with twice as much air as is theoretically needed, the 
products of combustion have 24.22 times the weight of the car- 
bon, and with hydrogen 80.56 times the weight of the hydro- 
gen. 



THE FUELS AND THEIR COMBUSTION. 



177 



AIR REQUIRED TO SUPPLY A DOUBLE AMOUNT OF OXYGEN. 



Carbon . . . 
Hydrogen. 



Parts by Weight 
ot Air. 



23.22 
79-56 



Volume of Air at 
60° F. per Lb. of 
Fuel, Cubic Feet. 



303 • 39 
908.62 



Parts by Weight of 
Gaseous Products. 



25.22 
80.56 



The Specific heat of air is 0.2377, and the quantities of heat 
needed to raise the temperature of the air demanded from 4°' 
to 5°, and the temperature resulting from combustion are : 

Combustion of carbon : 



and 



2.7597= ii-6i X 0.2377, 
8080 



2.759 + 2.975 



1408° C. 



and 



Combustion of hydrogen : 

34.78 X 0.2377 = ^.2672, 
29,629 



8.2672 + 10.8093 



= i553°C. 



It is evidently always desirable to secure perfect combustion, 
and with the least possible air-supply. With the forced draught 
produced by a fan or blast-pipe, fuel may be burnt with less air 
than with a chimney draught, and can be utilized with greater 
economy of heat. This economy is greater with fuel contain- 
ing but little volatilizable matter. 

Dissociation is a phenomenon which probably rarely if ever 
occurs in familiar practice. Oxygen and hydrogen, combined 
to form water, or steam, at ordinary furnace temperatures, are 
separated again by heat-energy when the temperature is some- 
where below 6000° Cent. (10,832° Fahr.). St. Claire Deville, the 
first to observe and study this phenomenon, concluded that dis- 
12 



I/S THE STEAM-BOILER. 

sociation may commence at 1000° Cent. (1832° Fahr.) or below 
that heat."^ Deville and Debray reported the temperature of 
the common oxyhydrogen flame to be not above 2500° Cent. 
(4532° Fahr.), and Bunsen found that under increasing pres- 
sures the temperature hmit as fixed by dissociation was raised 
until, at ten atmospheres, it had increased ten per cent or more. 

77. The Minimum Quantity of Air required for the per- 
fect combustion of any kind of fuel may be readily calculated 
from its known chemical constitution. 

CaUing the weight of air W, and denoting the weights of 
carbon, hydrogen, and oxygen, C, H, and O, 

lV^i2C+z6[l/-^) (4) 

The value of H^ ranges from 6 for dry wood, to 12 for an- 
thracite and good bituminous coal. Charcoal and the softer 
bituminous coals require about 1 1 parts by weight of air per i 
part of fuel. 

These values can only be approximated, in practice, with 
extremely slow and carefully managed combustion. A perfect 
intermixture of the combustible with the supporter of combus- 
tion can only be secured by the admission of some excess of air 
to the furnace. Probably about double the estimated amount 
of air is usually provided, although in some cases, where a 
forced draught produces exceptionally complete intermixture 
of the gases, the quantity may be brought as low as 18 pounds 
of air per pound of coal. 

In one instance, in which a furnace burning wet fuel was 
tested by the Author, to determine its economic efficiency, the 
quantity of air supplied was very little in excess of that dictated 
by theory. This was, however, an exceptional case. As the 
excess of air must be heated to the temperature of the chimney, 
and then thrown away, it causes a notable waste of heat. 

The weight of a cubic foot of air at mean atmospheric tem- 
perature being 0.076361 pound, the vohime of air required for 

Archives des Sciences Physiques, i860, t. ix. , p. 51. 



THE FUELS AND THEIR COMBUSTION. 1 79 

perfect combustion, in any case, may be determined by the 
equation : 



F=i57C+47i(^-x). 



(5) 



Eighteen and twenty-four pounds of air, required, as stated 
above for combustion, in the case mentioned, of one pound of 
coal, would measure, respectively, 236 and 314 cubic feet. 

The weight of a cubic metre of air is 1.224 kilogrammes. 
The volume, in metric measures, required in any case is there- 
fore 

F' = 9.8C+29(//-|-). ..... (6) 

When eighteen and twenty-four times the weight of fuel 
are required respectively, the volumes in the case taken would 
be 15 and 19 cubic metres. 

78. The Temperature of the Products of Combustion 
may be calculated, as has been shown, with approximation to 
accuracy, from the known weight of the fuel and of the prod- 
ucts of combustion, the heat-generating power of the former, 
and the specific heat of the latter. 

The specific heat of the products of combustion are, at con- 
stant pressure, and for equal weights : 

SPECIFIC HEATS OF PRODUCTS OF COMBUSTION. (REGNAULT.) 

{Water =i i. Pressure constant.') 

Air 0.2374 

Oxygen 0.2175 

Nitrogen . o . 2438 

Steam o . 4805 

Carbonic acid. 0.2164 

The proportions in which these substances occur in the prod- 
ucts of combustion being known, the mean specific heat of all 
may be determined ; and the total heat of combustion of one 
pound of fuel being divided by the product of this weight by 



l80 THE STEAM-BOILER. 

this mean specific heat, the quotient is the probable tempera- 
ture of the furnace gases. 

Rankine gives the result of this calculation, in cases where 
carbon alone is burned with undiluted air, and diluted with one 
half and with equal weight of additional air, respectively, 4580°, 
3215°, and 2440° Fahr., equal to 2627°, 1824°, and 1338° Cent. 

defiant gas, similarly treated, should give temperatures of 
5050°, 35 1 5°, and 2710° Fahr.; or 2788°, 1953°, and 1488° Cent 

The mean specific heat of the products of combustion is 
practically equal to the specific heat of air. 

The following are the specific heats given by Rankine : 

SPECIFIC HEAT UNDER CONSTANT PRESSURE. 

Carbonic-acid gas 0.217 

Steam o. 475 

Nitrogen, probably o. 245 

Air 0.238 

Ashes o . 200 

Durham (British) coke, having the composition (Deering) 
of— 

Carbon 93-78 • 

Sulphur 0.82 

Ash 5 . 40 

Total 100.00 

liberates 13,640 British thermal units per pound and requires 
10.91 pounds of air per pound of fuel, for complete combustion, 
the heat produced being 1145 units per pound, the resultant 
rise in temperature being 4877° F. (2709° C), and the amount 
of water evaporated, as a maximum, being 14.12 times the 
weight of the coke. 

The best bituminous coal contains, as an example, 

Carbon 81.47 

Hydrogen , 4.97 

Nitrogen i . 63 

Oxygen 5.32 

Sulphur , 1 . 10 

Ash 5.51 

Total c, , 100 00 



THE FUELS AND THEIR COMBUSTION. l8l 

Its complete combustion requires 10.99 times its weight of 
air, giving a rise of temperature of 4830° F. (2683° C.) and an 
evaporation of 14.64 times its weight of water from and at the 
boiling-point. The heat produced is 14,143 units per pound 
of fuel, or 118° per pound of furnace gases. 

Oak wood, according to Deering,"^ has the composition, 
when kiln-dried, 

Oxygen 41-27 

Hydrogen 6 . 00 

Nitrogen i . 13 

Carbon 49-95 

Ash 1.65 

Total 100 . 00 

It will evaporate 7.98 times its own weight of water, develop- 
ing 7713 British heat-units per pound, demanding 6.08 times 
its own weight of air for complete combustion, the products of 
combustion containing 1089 heat-units per pound and attaining 
a temperature of 4287° F. (2382° C). 

Pennsylvania petroleum, having the composition, according 
to Deerine, of 



'fc>> 



Carbon 85 J Hydrogen 15 

requires 15 times its own weight of air for complete combus- 
tion, liberates 20,360 British thermal units per pound of the 
liquid, or 1267 per pound of products of combustion, and de- 
velops an increase of temperature of 4900° F. (2722° C). 

Illuminating gas, according to Mr. Deering, having the 
composition. 

Carbon 61.26 

Hydrogen 25 .55 

Nitrogen 8.72 

Oxygen 4.47 

Total 100.00 

develops 20,801 British thermal units per pound, equivalent to 

* Howard Lecture. W. Anderson. London, 1885. 



1 82 THE STEAM-BOILER. 

the evaporation of 21.53 times its own weight of water, the 
best mixture for complete combustion being 15.66 parts of air, 
by weight, to one of the gas. The rise in temperature with 
perfect combustion is 4567° F. (2537° C), the total heat liber- 
ated being 1250 British thermal units per pound of the mix- 
ture. 

The same gas, per 1000 cubic feet, weighs as follows : 

Carbon 18.19 lbs. 

Hydrogen « 7.58 ** 

Nitrogen , 2.59 " 

Oxygen 1.33 ** 

Total „ 29 . 69 lbs. 

It produces 617,485 units of heat, and can evaporate 639 pounds 
of water, demanding 465 pounds of air for complete combus- 
tion. 

By using the data of Rankine, results are obtained for the 
two extreme cases oi pure carboji and olefimit gas, burned re- 
spectively in air ; British units are used thus : 

Carbon. Olefiant Gas^ 

Total heat of combustion per pound 14,500 21,300' 

Weight ot products of combustion in air, undiluted 13 lbs. 16.43 lbs. 

Their mean specific heat 0.237 0.257 

Specific heat X weight 3.08 4.22 

Elevation of temperature, if undiluted 4,580° 5,050° 

If diluted with air = -J air for combustion. 

Weight per lb. of fuel. . . 19. 24.2 

Mean specific heat 0,237 0.25 

Specific heat X weight 4.51 6.06 

Elevation of temperature 3,215° 3,515** 

If diluted with air = air for combustion. 

Weight per lb. fuel 25. 31.86 

Mean specific heat o. 238 o. 248 

Specific heat X weight 5 . 94 7,9 

Elevation of temperature 2,440° 2,710° 

For wet fuel, like sawdust, or spent tan from the leach, the 
Author has made the following estimation in one actual case 



THE FUELS AND THEIR COMBUSTION. 1 83 

where the fuel consists of 45 per cent of woody fibre, and 55 
per cent of water. 

Taking the available heat per pound of the dry portion at 
6480 British thermal units, each pound of wet fuel yields 2916 
units of heat. Of this, 531.6 are absorbed in the evaporation 
of the 55 per cent of water, leaving 2384.4 units to raise the 
temperature of the products of combustion. Of these there 
are, as a minimum, 3.7 pounds, having a mean specific heat of 
about 0.287. 

The elevation of temperature is therefore 2245.3° Fahr., 
and adding the mean temperature of the atmosphere, 74°, the 
mean temperature of furnace, assuming no dilution with un- 
used air, and no losses, would have been about 2320° Fahr. 
(1271° Cent.). Losing 2\ per cent by radiation and conduc- 
tion, etc., the actual temperature was 2260° Fahr. (1238° Cent.). 

The temperature of chimney flue was found by experiment 
to have been 544°. The furnace gases were therefore cooled 
2260° — 544° = 1716° Fahr. (937° Cent.) by the loss of the 
heat given up to the boiler. This is equivalent to 1716X0.287 
= 492.5 British heat-units per pound of gas, and to 4049.4 
units per pound of ligneous material in the fuel. 

The " equivalent evaporation," from and at 212°, is 4049.4 
-^ 966.6 = 4.18 pounds of water. The actual evaporation was 
equivalent to 4.24 pounds, and the difference — less than one per 
cent of the total — represents losses and errors of calculation. 

The actual existing temperature of furnace can be also thus 
estimated. The available heat per pound of fuel, including 
water, has been given at 2916 British thermal units. Of this 

531.6 

-p- =: 0.182 passed off with vapor, and was not useful in rais- 
ing the temperature of either the furnace or the chimney. 
Hence, of all heat liberated, i. 00 — 0.182 = 0.818 was efficient 
in elevating the temperature of furnace, and 0.37 — 0.182 
= 0.188 was effective in producing the observed temperature, 
544° Fahr., of chimney. Then, since the same quantity of 
gas passes at both places, the temperature of furnace was 

(0T88 ^ "^^^ + 74° = 2119° Fahr. To this is to be added 



1 84 THE STEAM-BOILER. 

the slight loss of temperature en route between furnace and 
chimney by conduction and radiation, which may make the 
figure very nearly 2260° Fahr., as above. 

The actual temperature of the furnace may be judged, in 
any case, by observing the brilliancy of the light radiated from 
any solid in its midst, and presumably at its own temperature, 
as by the following table given by Pouillet : 

Appearance. Temp. Fahr. 

Red, just visible 977" 

" dull , ,. 1290 

" cherry, dull 1470 

full 1650 

" " clear 1830 

Orange, deep .... 2010 

" clear 2190 

While heal 2370 

" bright 2550 

" dazzHng 2730 

To determine temperature by fusion of metals, we have 
also from the same authority — 

Substance. Temp. Fahr. 

Tallow .... 92° 

Spermaceti 120 

Wax. while 154 

Sulphur 239 

Tin 455 

Metal. 

Bismuth 518 

Lead 630 

Zinc 793 

Antimony 810 

Brass ' 1650 

Silver, pure 1830 

Gold coin 2156 

Iron, cast, medium 2010 

Steel 2550 

Wrought-iron 2910 

79. The Rate of Combustion is determined principally 
by the quantity of air supplied. The amount of coal burned 
per square foot of grate with chimney draught varies very 



THE FUELS AND THEIR COMBUSTION. 1 85 

nearly with the square root of the height of the chimney, and 
has been found by the Author, ordinarily, to be very nearly, as 
a maximum, 

W=2V'H-\, or ^^=17^^^-0.5, 

where W and W are weights of fuel burned per hour per 
square foot of grate, and on the square metre, in pounds and 
kilogrammes, and H and H' are the heights of chimney in feet 
and metres. 

A chimney 64 feet or \C)\ metres high, will, for example, 
tinder favorable conditions, usually support combustion of 15 
pounds of coal per square foot of grate, or of 73 kilogrammes 
per square metre. The weight of combustible which may be 
burned in any unit of time may be calculated approximately 
by dividing the weight of air which can be supplied in that 
time, by its proportion to weight of fuel, as determined in the 
preceding paragraphs. In exceptional cases there is sometimes 
a large excess of air, and sometimes a considerable deficiency. 
In such instances, direct experiment only can determine the 
amount of fuel burned. 

80. The Efficiency of the Furnace, considered as a heat- 
titilizing apparatus, is determined by the temperature of fur- 
nace gases, by the thoroughness with which complete combus- 
tion is secured, and with which losses of fuel and of heat are 
prevented. It is measured by the ratio of the amount of the 
total available heat of the fuel to that of the heat actually util- 
ized. This efficiency is rarely so high as 80 per cent, and fre- 
quently falls to 50 per cent. 

In all cases, efficiency is to be studied, in applications of 
heat, in two parts: (i) the efficiency of the heat-generating and 
absorbing apparatus, i.e., the furnace ; (2) the efficiency of the 
heat-utilizing apparatus and methods, as the steam-boiler, the 
heating-chamber of the reverberatory furnace, or such other 
heat-absorbing arrangement as may be adopted. 

(i) The efficiency of the furnace is represented by 

T — T 
F — -^ — ' 

r, - t: 



I 86 THE STEAM-BOILER. 

in which E is the ratio of the heat rendered available to heat 
developed ; 1\, T^, T^, are the temperatures of furnace, of 
chimney, and of external air. For examples, in two actual 
cases, T,, T^, 7;, were, 2118° F., 544° F., and 74° F., or 1176°, 
302°, or 510°, 251°, and 48° C. for the second case. The values 
of the efficiencies of the two kinds of apparatus were 



2118° - 544° 

2118° - 74°-°-^^' 


and 


919° - 452° ^ . 
9i90_g6^^-o = o.56, 


or for Centigrade degrees, 






1176° — 302° 

1176° - 41°-°-^^' 


and 


510° — 251° ^ 
510°- 48°" ^''•^^' 



the first being nearly 40 per cent higher than the second. A 
certain change of fuel would have given the first a maximum 
temperature of 2644° F., 1451° C, and would have raised its 
efficiency to 

2644° - 544° _ ^ 
~o — o.oi, 



2644° - 74^ 



or 



1451° - 279° 



:45i^ - 23 



= 0.81, 



(2) The efficiency of the heat-absorbing apparatus is de- 
pendent upon the character and proportion, and is not treated 
here. The highest efficiency in heat-production is secured by 
perfect combustion with the least practicable air-supply, thus 
obtaining the highest possible resulting temperature. 

A large part of the heat produced by combustion of fuel 
is expended in procuring chimney draught. This is not avail- 
able for producing any other useful effects. 

The amount of heat thus expended varies with the nature 
of the products of combustion, and the use to which the heat 



THE FUELS AND THEIR COMBUSTION. 1 8/ 

is to be applied. In all cases the heat thus discharged is 
wasted. 

The temperature of the products of combustion cannot 
usually be reduced much below about 600° F., or 315° C. 

81. Economy in Combustion of Fuels, where they are 
used simply in the production of high temperature, is so im- 
portant a matter, except in those favored localities where the 
proximity of coal, or of peat-beds, or of forests, renders its 
waste less objectionable, that the engineer should omit no 
precaution in the endeavor to secure their perfect utiliza- 
tion. 

To secure the greatest economy, it is necessary to adopt a 
form of grate which, while allowing a sufficient supply of air 
to pass through it to insure complete combustion, has such 
narrow air-spaces as to prevent waste of small fragments, by 
falling through them. 

The narrower the grate-bars and the air-spaces, the more 
readily can losses from this cause and from obstruction of 
draught be avoided. With a hot fire, however, the difficul- 
ties arising from the warping of the bars become so great, 
that it is only by peculiar devices for interlocking and bracing 
them that their thickness can be reduced below about -§■ of an 
inch at the top. Many such devices are now in use. In fur- 
naces burning wet fuel, with an ash-pit fire, fire-brick grate-bars 
are used. 

A certain amount of air must usually be allowed to enter 
the furnace above the grate, to consume those combustible 
gases which do not obtain the requisite supply of oxygen from 
below. The carbon, probably, in such cases usually obtains 
its oxygen from below the grate, while the gaseous constituents 
of the fuel are consumed by the oxygen coming in above. 

Chas. Wye Williams, who made most extended and care- 
ful experiments on combustion of fuel, recommended, for 
ordinary cases, where bituminous coal was burned, a cross area 
of passage, admitting air above the grate, of one square inch 
for each 900 pounds of coal burned per hour, or about one 
square centimetre for each 63 kilogrammes of fuel. This area 
should be made larger, proportionally, as the thickness of the 



1 88 THE STEAM-BOILER, 

bed of the fuel is increased, and as the proportion of hydrocar- 
bons becomes greater. 

ChilHng the gases, before combustion is complete, should 
be carefully prevented ; and comparatively cold surfaces, as 
those of a steam-boiler, should not be placed too near the 
burning fuel. A large combustion-chamber should, where 
possible, be provided, and more complete combustion may be 
expected in furnaces of large size, lined with fire-brick, and 
with arches of the same material, than in a furnace of small size 
where the fire is surrounded by chilling surfaces, as in a *' fire- 
box steam-boiler." 

Finally, the greatest possible amount of heat being devel- 
oped in combustion, careful provision should be made for com- 
pletely utilizing that heat. 

In a steam-boiler this is accomplished by having large heat- 
ing-surfaces, and by so arranging the distribution of the 
adjacent currents of water and of hot gases that their differ- 
ence of temperature shall be the greatest possible. The gases 
should enter the flues at that part of the boiler where the tem- 
perature is highest, and leave them at the point of lowest tem 
perature. The feed-water should enter as near as possible to 
the point where the gases pass off to the chimney, and should 
gradually circulate until evaporation is completed at, as nearly 
as possible, that part of the boiler nearest to the point of 
entrance of the heated gases. 

Where a small combustion-chamber is unavoidably employ- 
ed, as in locomotives, various expedients have been devised 
with the object of producing complete intermixture of gases 
before entering the tubes. The most common and most suc- 
cessful is a bridge-wall, sometimes depending from the crown 
sheet, but sometimes rising from the grate, and which, by the 
production of eddies in the passing current, causes a more 
thorough commingling of the combustible gases with the 
accompanying air. None of these devices seem yet to have 
given such good results as to induce their general adoption. 

In the furnaces of steam-boilers it is usually considered 
advisable to allow the gaseous products of combustion to enter 
the chimney at a temperature of about 600° Fahr. (315° Cent.), 



THE FUELS AND THEIR COMBUSTION. 1 89 

or about 2.08 times the absolute temperature of the external 
air, where natural draught is employed. Rankine has stated 
that the best temperature of chimney for natural draught is 
that at which the gases have a density equal to about one half 
that of the external air. Thus, the temperature of the external 
air being 60° Fahr. (15°. 5 Cent.), its absolute temperature is 
521°. 2 (261°. 75 Cent.), and the required absolute temperature 
of the gases in the chimney will be this temperature multiplied 
by 2jL-, i.e., 521°. 2 X ^t2 — 1085°. 8, and the corresponding 
temperature on the ordinary scale is 624° .6 Fahr. (339°. 2 Cent.). 

With forced draught, a considerable economy may be 
effected by the reduction of the temperature of escaping gases 
approximately to that of the boiler itself at the point of dis- 
charge of the gases. 

The fuel should be usually burned at a fair rate of combus- 
tion, and in such manner as to give that degree of efficiency 
which has been found financially desirable. The air-supply 
should be provided for, partly above as well as below the 
grates, bituminous coal demanding more above the bed of fuel 
than anthracite, partly because it is needed to burn the gaseous 
hydrocarbons driven off from the former, and partly because 
the bituminous fueMs burned in a thicker and less permeable 
bed of fuel. Ten or fifteen per cent of the total air-supply 
should usually be furnished above the flame-bed. 

The grate-area should always be so proportioned that it 
shall be possible to keep it, in ordinary working, at all times 
well and uniformly covered with incandescent fuel. The 
space above the grate, between it and the heating-surfaces, 
should always be so large that ample space and time are given 
for thorough intermixture of gases and complete combustion, 
and it should have such form that the air introduced above 
the fuel may become well mingled with the gases distilled 
from the coal. The effect of this air-supply, where bituminous 
coal is used, is well shown in an experiment by Mr. Houlds- 
worth,^ made in 1842 for the British Association, at its Man- 



* Fuel Combustion and Economy; C. W. Williams. " On the Consumption of 
Fuel, etc.;" Wm. Fairbairn, Trans. Brit. Assoc. 1842. 



190 



THE STEAM-BOILER. 




Air admitted \ 

State of tho 

Flues. 

( Clear flame, \ 
\ 14 feet long. / 



Ditto, 15 ft. long. 



M 




Ditto, 


16 feet. 


t^ 


Ditto, 


15 feet. 


r4^ 




Ditto, 


14 feet. 




Ditto, 


13 feet 


§ 







S Ditto, 13 feet. 



flame, \ 
rbonic > 
de. ) 



^ Ditto, 15 feet. 
QQ I Purple flame, 
o * I from carbonic 
oo ( oxide. 



CO O O fcO 
O O fcO CO 

0000 
00 00 

'papmoxa .ire -pa^^tunpB are 
'ucid "pio tio 'acid Aiau uq 

Fig. 69.— Temperature of Furnace. 



Chester meeting. As seen by reference to Fig. 69, the tem- 
perature in the flue fell to 750° F. (400° C.) on the introduc- 
tion of a fresh charge of fuel, rose at the end of a half-hour 



THE FUELS AND THEIR COMBUSTION. IQI 

to above 1200° F. (650° C), then fell, until at the end of an hour 
and a quarter it had dropped to 1040° F. (560° C), the fire 
meantime not having been disturbed. On then levelling off 
the Surface of the bed of fuel, and thus filling all holes in the 
fire, the temperature at once rose nearly to the maximum, and 
then gradually fell again to 850° F. (454° C). During this 
period, the air was admitted above the fire ; the lower line of 
the diagram shows the result of the usual method of handling 
the fires without air-supply above the fuel. The general 
method of variation of temperature is the same during the 
period between successive charges, but the temperature averages 
ten per cent lower. The transformation of a mass of black 
smoke into a flame many feet in length is the best possible 
evidence of the advantage of this operation. The gain in 
economy of fuel was estimated at about one third when the 
supply of air was properly adjusted and managed. The dotted 
line in the figure indicates the probable temperatures when the 
bed of fuel is kept level and free from holes. 

82. Weather Waste. — When coal is exposed to atmos- 
pheric influences, a '' weather waste " occurs. Oxygen is 
absorbed, and a slow combustion injures the fuel. Berthelot 
found also that at temperatures not exceeding 530° Fahr. 
(277° Cent.) hydrogen may be absorbed, and succeeded in 
converting two thirds of the bituminous coal experimented 
with into liquid hydrocarbons. Coals freshly mined give out 
gaseous hydrocarbons, and even anthracite mines, where deep, 
are not free from danger by the explosion of such gases. The 
absorption of oxygen, and this loss of hydrogen and carbon, is 
injurious to the fuel. According to Mursiller, coals containing 
" fire-damp" give it up at or below 626° Fahr. (330° Cent.), 
and lose their coking property. Coals usually absorb carbonic 
acid freely. 

Poech concludes r^ '' Freshly-mined coal deposited on the 
rubbish piles is capable of condensing several times its volume 
of oxygen in its pores. The oxygen absorbed enters into 
chemical combination with the easily-oxidized constituents. 

* Van Nostrand's Magazine, 1884. 



192 



THE STEAM-BOILER. 



According as the absorption is rapid or slow, a greater or less 
elevation of temperature is produced. In the former it may 
lead to spontaneous combustion. The crumbling of coal is, 
among other causes, a consequence of the absorption and con- 
densation of oxygen in its pores, and the chemical changes tak- 
ing place. The escape of the hygroscopic moisture favors the 
absorption of oxygen. The pyrites can only produce a further- 
some effect on the increase of temperature when present in 
considerable quantities, and then only in presence of moisture 
and air ; in the dry state they must be regarded as perfectly 
passive, and may even be detrimental to the warming. Freshly- 
mined coal placed in an atmosphere of steam can suffer nO' 
change. Even with incomplete exclusion of the air the steam 
will, in general, oppose oxidation and warming, principally by 
uniform moistening of the pieces of coal." 

83. The Composition of the Common Fuels may be ob- 
tained from the following tables : 



COMPOSITION OF VARIOUS FUELS OF THE UNITED STATES. 





C. 


H. 0. 


N. 


3-. 


Mois- 
ture. 


Ash. 


Spec. 
Grav. 


Pennsylvania Anthracite 

Rhode Island " 

Massachusetts " 

North Carolina ** 


78.6 

85.8 
92.0 
83.1 

84.2 
80.5 

75.8 
59-4 
70.0 
52.0 
62.6 
58.2 
59-5 
48.4 
71.0 
41-5 

55-0 
74.0 

50.1 


2.5 1-7 

10.5 
6.0 

7.8 

3-7 2.3 

4.5 2.7 

20.2 

38.8 
28.0 
39-0 
35-5 
37-1 
36.6 
48.8 
17.0 
56.5 
42.6 
41.0 
18.6 

^ A ^ 

3.9 13-7 


0.8 

0.9 
I.I 


0.4 

3-7 
2.0 
9.1 

0.9 
1.2 


1.2 


14.8 


1.45 

1.85 
I.7& 


Welsh '* 

Maryland Semi-Bituminous 

Penna. " *' 


1-3 

1.7 


6.7 
8.3 

4.0 
1.8 
2.0 
9.0 
1.9 
4.7 
3-9 
2.8 
12.0 

2.5 
1.2 
4.0 
7-4 

13.2 


1.40 
1-33 

1.32 
1.30 
1.24 
1.27 
1.30 


1 ( <( <( 








Indiana " " 








Illinois Bituminous 








(Block) Bituminous . 

Ill and Ind. (Cannel) Bituminous 

Kentucky 

Tennessee Bituminous 














1.27 
1.25 
1.45 






















Alabama " 




I.O 


1.2 




Virginia " 








Cal. and Oregon Lignite 


0.9 


1.5 


16.7 


1.32 



THE FUELS AND THEIR COMBUSTION. 



193 



MONONGAHELA GAS COAL. (CRESSON.) 

Weight of sample, 60 lbs. (27.27 kilogrammes). 

V.olatile matter, per cent 35-74 

Coke, per cent 64 . 26 

Ash, per cent 6.66 

Yield of gas, cubic feet per pound maximum 5.2 

" *' cubic metres per kilogramme maximum. . . . 0.324 

Cubic feet per pound average 5.0 

" ** cubic-metres per kilogramme average 0.312 

Ton maximum , 11,648.0 

" average 11,200.0 

Illuminating power, 5 feet per hour = candles 15.0 

** ** I ton coal = lbs. sperm 576. 0' 



COMPOSITION OF FOREIGN COALS. 



Welsh (Anthracite) 

Scotch " 

English (Newcastle). . . 
(Lancashire)... 

" (Derbyshire).. . 

" (Staffordshire). 
French Anthracite . . . 

" Bituminous. . . 

Spanish (Asturias) 

German (Silesia) 

Saxony 

Prussia 

Hindostan 

Brazil 

Nova Scotia 

Cape Breton 

Australia (Lignite) 

Borneo 

Chili 

Coke 

13 



90.4 

78.5 
82.1 

77-9 
79-7 
78. 6 
94.0 
84.0 



64-3 
70.3 
70.6 

91-5 



H. 



4.2 

5-4 

5-8 



0.8 
i.o 

1.4 

1-3 
1.4 
1.8 
0.6 
1.0 



o. 



Ash, 



0.9 
1. 1 
I .2 
1.4 
1.0 
0.4 



40.0 
42.0 
19.0 
18.9 

35-4 
40.5 
26.8 
26.9 



1.0 
0.7 
1.0 



13.2 



I 

4 

3 

4 

2 

I 

4.0 

2.0 

7.0 

2.1 

1.0 

24.4 

14.6 

1.6 

12.5 

5-5 



0.6 10. o 

1.2 14.2 
2.0 7.4 
1.5 7.0 

I 



Specific 
Gravity. 



Authority. 



1.32 
1.26 
1 .26 
1.27 
1.29 



1-33 



.26 



1.27 

1.37 
1.29 



Vaux. 
Muspratt. 



Vaux. 

Jacqueline. 

Ledieu. 

Johnson. 



Isherwood, 
Muspratt. 



194 



THE STEAM-BOILER. 



COMPOSITION OF SUNDRY FUELS. 



Wood (kiln-dried) 

" (air-dried) 

Peat (kiln-dried) 

• (air-dried) 

Bitumen, United States... 

" England 

" France 

" South America. . 
Asphaltum, Syria 

Petroleum, pure U. S 

''Dead Oil" 

Gas, Marsh 

" defiant 



50.5 
40.4 
60.0 
46.1 



24.8 
52.2 

50.3 
71.8 
24.4 
14.0 
86.0 



86.5 
75-0 

85.7 



H. 


N. 


0. 


0. I 


.... 


40.7 


4.9 


0.9 


32.7 


6.8 


1-3 


30.0 


4.6 


I.O 


23.6 



Volatile Matter. 



72, 

47 
41, 
26, 

68, 
72, 
14 



Ash, 



1.6 
1.2 

1.9 

1-5 



2.8 

0.3 
0.1 

1.5 

7-6 
13.6 



Specific 
Gravity. 



0.5 to 1,2 
0.5 



7.0 
25.0 
14-3 



Refuse. 



1-5 



0.8 



Authority. 



Watts. 
Paul. 



Johnson. 



Watts. 





Carb. 

Acid. 


Carb. 
Oxide. 


H. 


N. 


Hydro- 
carbon. 


Authority. 


Gas from Wood 


II. 6 

0.8 

14.0 

1-3 
2.0 

4-1 


34-5 
34-1 
22.4 
33.8 
40.0 
23.7 


0.7 
0.2 

0.5 

O.I 

42.4 

8.0 


53-2 

64.9 

63.1 
64.8 

3-2 

61.5 


12.4 
2.2 


Ebelmen. 


'• Charcoal 




" Peat 

" Coke 


<( 


" " Lignite .... 

** " Bituminous Coal*. 


Siemens. 



* Burned in Siemens' gas-producers. 



84. The Heating Effect, or calorific power of good 
specimens of the various kinds of fuel, is given in the follow- 
ing table, expressed in British thermal units : 



THE FUELS AND THEIR COMBUSTION. 



195 



CALORIFIC VALUE OF FUELS. 



Fuel. 



Carbon, pure 

Hydrogen 

Marsh gas 

Olefiant gas 

Coal, Anthracite 

" Bituminous 

" Lignite, dry 

Peat, kiln-dried 

" air-dried 

Wood, kiln-dried 

" air-dried 

Charcoal 

Coke 

Petroleum, heavy. W. Va. 
light, W. Va... 
" Penna.. 
heavy, Ohio. . . 

Asia 

Europe 

Shale Oil, France (crude). . 
Animal fat 



Calorific Power. 



Relative. Absolute 



000 

280 

816 

466 

020 

017 

7 

7 

526 

551 

0.439 
0.930 
0.940 
1.250 
1.260 
1.240 
1.270 
1.240 
1.240 
1.240 
0.650 



14,500 
62,500 
26,415 
21,328 
14,833 
14.796 
10.150 
10,150 
7,650 
8,029 
6.385 
13,500 
13,620 
18,200 
18,350 
18,050 
18,450 
18,000 
18,000 
18,000 
9,000 



Water 
vaporized 
at Boiling- 
point, 
Parts by 
one Part. 



15. 
62. 
26. 
21, 
14, 
14, 
10. 
10, 

!■ 

%. 

6. 

14 

14 

18, 
18 
18. 
19 
18, 
18 
18, 



Cubic Feet 

required 

to stow 

one Ton 

of Furnace 
Coal. 



40 to 45 
42 to 48 

42 
81 

75 



56 to 100 

56 to 75 

45 



Weight. 
Pounds 
per Cubic 
Foot as 
stowed. 



49 to 56 
47 to 53 

53 

25 

30 

22 to 40 

30 to 40 
50 



The difference between theoretical and effective heating 
power for various kinds of fuel is exhibited in the following 
table, which gives the number of pounds of water evaporated 
by one pound of fuel, according to European authorities : 





Heating Power. 


Fuel. 


Theoretical. 


Under 
Steam Boilers. 


Under 
Open Boilers. 


Petroleum 


16.30 
12.45 

II. 51 

10.77 

9.0 to 10.8 

7-7 

5.5 to 7.4 

4.3 to 5.6 

3-0 


10. to 14.0 

7.0 to II.O 

5.2 to 8.0 
6.0 to 6.75 
5.0 to 8.0 
2.5 to 5.5 
2.5 to 5.0 
2.5 to 3.75 
1.86 to 1.92 




Anthracite 




Bituminous Coal 

Charcoal 


5-2 
3-7 


Coke 


Lignite , 


1.5 to 2.3 
1.7 to 2.3 

1.85 to 2.1 


Peat 

Wood 


Straw 



196 



THE STEAM-BOILER. 



RELATIVE VALUE OF VARIOUS WOODS. (OVERMAN.)* 



Wood. 



Specific 
Gravity. 



Hickory, shell bark i .000 

Oak, chestnut 0.8S5 

" white 0.885 

Ash, white .. 0.772 

Dogwood 0.815 

Oak, black o . 728 

" red 0.728 

Beech, white o . 724 

Walnut, black 0.681 

Maple, hard (sugar) 0.644 

Cedar, red j 0.565 

Magnolia i o . 605 

0.597 
0.551 
0.535 
0.567 
0.478 
0.426 
0.41S 
0.397 
0.552 
0.563 



Maple, soft. 

Pine, yellow 

Sycamore 

Butternut 

Pine, New Jersey. . . . 

" pitch 

" white 

Poplar, Lombardy. . . 

Chestnut 

Poplar, yellow... .... 



Pounds 
in one 
Cord. 



4,469 

3.955 
3-821 
3,450 
3,643 
3,254 
3.254 
3,236 
3.044 
2,878 

2.525 
2.704 
2,668 
2,463 
2,391 
2-534 
2.137 
1.004 
1.868 
1.774 
2,333 
2,516 



Per- 
centage 
Charcoal. 



26.22 

22.75 
21 .62 

25-74 
21.00 
23.80 
22.43 
19.62 
22.56 
21.43 
24.72 
21.59 
20.04 

23-73 
23.60 
20.79 

24.88 
26.76 

24.35 
25.00 
25.29 
21.81 



Specific 
Gravity of 
Charcoal. 



0.625 
0.481 
0.401 
0.447 
0.550 
0.387 
0.400 
0.518 
0.418 
0.431 
0.238 
0.406 
0.370 

0.333 
0.274 
0.237 

0.385 
0.298 
0.293 
0.245 
0.379 
0.383 



Pounds of 
Charcoal 
in a Bush. 



32.89 

25.31 
21 .10 
28.78 
29.94 
20.36 
21.05 
27.26 
22.00 
22.68 

12.52 
2T.36 
19.47 
17-52 
19.68 
12.47 

20.26 
15-68 
15.42 
12.85 
19.74 
20.15 



Relative 

Value 

of Wood. 



1. 00 
0.86 
0.81 
0.77 

0-75 
0.71 
0.69 
0.65 
0.65 
0.60 
0.56 
0.56 
0.54 



54 

52 

51 

48 

43 

0.42 

0.40 

0.52 

0.52 



* Metallurgy. N. Y. : D. Appleton & Co., 1864. 

Wood cut in January contains from 15 to 25 per cent less 
water than after the sap is in motion in April. As wood 
seasons naturally in the air, it loses from one sixth to one 
third its weight of water, but still contains from one seventh 
to one fourth its weight of moisture. A considerable part of 
the latter may be expelled by kiln-drying, and most of it if the 
kiln heat be raised to 212°. A cord of wood contains 128 
cubic feet as it lies piled up. But allowing for the interstices 
in fairly piled wood, we may reckon a cord to actually contain 
about seventy-two cubic feet. Thoroughly dry wood weighs 
nearly as follows : 

One cubic foot. One cord. 

Hickory, pounds 62 4,464 

White oak 53 3,816 

White ash 49 3,528 

Red oak 45^ 3,276 

White beech 45 2,240 



I 



THE FUELS AND THEIR COMBUSTION. ' IQ/ 

One cubic foot. One cord. 

Apple tree 43 3.096 

Black birch 43 3,096 

Black walnut 42^ 3,060 

Hard maple 40 2,880 

Soft maple 37 2,664 

Wild cherry 37 2,664 

White elm 36^ 2,628 

Butternut 35i 2,556 

Red cedar 35 2,520 

Yellow pine » ^34 2,447 

White birch 33 2,376 

Chestnut 32 2,304 

White pine 26 1,872 



With hickory at $5 a cord, other woods are worth about as 
below : 

Hickory $5 00 

White oak 4 05 

White ash 3 85 

Apple 350 

Red oak — 4 45 

White beech 3 25 

Black walnut 3 25 

Black birch 3 15 

Hard maple 3 00 

White elm 2 90 

Red cedar 2 08 

Wild cherry 2 75 

Soft maple 2 70 

Yellow pine '. 2 70 

Chestnut 2 60 

Butternut 2 55 

White birch 2 40 

White pine 2 10 

Experiments on combustion, conducted by MM. Scheurer- 
Kestner and Meunier-Dollfus,^ indicate that the method em- 
ployed for determining the heating power of fuel, from its 
analysis, is not correct. A satisfactory explanation of this 
difference has not been given. The heating effect may depend 

* Bzdletiii de la Societe Industrielle de Alulhouse^ 1868, 1869, 



iq8 



THE STEAM-BOILER. 



on the state in which the carbon exists in the coal ; and that 
although the calorific effect of the combustion of charcoal has 
been determined, it may be higher in the case of other forms 
of carbon.* 

Mr. G. H. Babcock gives the following tables as representa- 
tive of familiar practice : 





Air 
Re- 
quired. 


Temperature of 
Combustion. 


Theoretical 

Value, 


Highest 

attainable 

Value under 

Boiler, 


Kind of 
Combustible. 




II 


'It 


With ii^ Times the 
Theoretical Supply 
of Air. 


With Twice the.The- 
oretical Supply of 
Air. 


% 

1.940 
1,850 

1,650 

1,730 
1,810 

1,720 
1,670 

1,660 

1,550 

1,530 

1,490 


ill 


In lbs. of water evap- 
orated from and 
at 212°, with I lb. 
combustible. 


c 


With Blast. Theo- 
retical Supply of 
Air at 60°, Gas 
320". 


Hydrogen 

Petroleum 

CarDon — 

Charcoal 

Coke - 

Anthracite C'l 

Coal- 
Cumberland .. . 
Coking bitumi- 
nous 


36.00 
15-43 

12.13 

12.06 
11-73 

11.80 
9-30 

7.68 

5-76 

6.00 

4.80 


5,750 
5,050 

4,580 

4,900 
5,140 

4,850 
4,600 

4-470 

4,000 

4,080 

3,700 


3,860 
3,515 

3,215 

3,360 
3,520 

3,330 
3,210 

3,140 

2,820 

2,910 

2,670 


2,860 
2,710 

2,440 

2,550 
2,680 

2,540 
2,490 

2.420 

2,240 

2,260 

2,100 


62,032 
21,000 

14.500 

15.370 
15,837 

15,080 
",745 

9,660 

7,000 

7,245 
5,600 


64.20 
21.74 

15.00 

15.90 
16.00 

15.60 
12.15 

10.00 

7-25. 

7 -50! 

5.80 


18.55 

13-30 

14.28 
14-45 

14.01 
10.78 

8.92 

641 

6.64 

4.08 


19.90- 

14.14. 

15-06 
15 -ig 


Cannel 


14.76 
11.46 

9.42 

6.7& 

7 02 

4-3^ 


Lignite 

Peat— 

Kiln-dried 

Air-dried, 25 p.c. 

water 

Wood- 

Kiln-dried 

Air-dried,2op.c. 
water 



The above table gives the air required for complete com- 
bustion, the temperature attained with different proportions of 
air, the theoretical value, and the highest practically attainable 
value under a steam-boiler, assuming that the gases pa^s off at 
320°, the temperature of steam at 75 lbs. pressure, and the in- 
coming air at 60° ; also, that with chimney draught twice, and 
with forced blast only, the theoretical amount of air is required 
for combustion. 

The effective value of all kinds of wood per pound, when 



* M. L. Gruner, Engineering and Mining Journal, xviii. 



THE FUELS AND THEIR COMBUSTION. 



199 



dry, is substantially the same. The following are the weights 
on other authorities of different woods by the cord : 

Kind of Wood. Weight. 

Hickory, shell-bark 4,469 

red heart 3.705 

White oak , 3,821 

Red oak 3,254 

Beech 3.126 

Hard maple 2,878 

Southern pine 3,375 

Virginia piifi . 2,680 

Spruce 2,325 

New Jersey pine .c 2,137 

Yellow pine J. 904 

White pine - 868 

The following table of American coals has been compiled 
from various sources : 



Coal. 



KIND OF COAL. 



Pennsylvania Anthracite. 



Cannel 

Connellsville . . . . 

Semi-bituminous, 

Stone's Gas 

Youghiogheny. . . 

Brown 

Kentucky Caking 

" Cannel 



Lignite 

Illinois Bureau County . 

" Mercer County , 

" Montauk 

Indiana Block 

" Caking 

" Cannel 

Maryland Cumberland. . . 

Arkansas Lignite 

Colorado " 



Texas " . . . 

Washington Ter.. . . " . . . 
Pennsylvania Petroleum 



Per Cent of 
Ash. 



3-49 
6,13 
2.90 

15.02 
6.50 

10.77 
5.00 
5.60 



5. 
6. 

13. 
5- 
9- 
4- 
4. 
3 40 



Theoretical Value- 



Id Heat Units. 



14,199 

13.535 
14.221 

13,143 
13,368 
13,155 
14,021 
14-265 
12.324 
14-391 
15.198 
13,360 
9.326 
13.025 
13,123 
12,659 
13.588 
14.146 
13.097 
12,226 

9,215 
13.562 
13,866 
12,962 

11,551 
20,746 



In Pounds 

of Water 

Evaporated. 



14.70 
14.01 
14.72 
13.60 
13.84 
13.62 

14.51 
14.76 

12.75 
14.89 
16.76 
13.84 
9-65 
13.48 
13-58 
13. 10 
14.38 
14.64 
13-56 
12.65 

9-54 
14.04 

14.35 
13-41 
11.96 
21.47 



200 THE STEAM-BOILER. 

Mr. D. K. Clark thus assigns the several portions of the 
heat of combustion of good coke, as burned in the locomotive :^ 

Making steam 10,920 B. T. U. 73 per cent. 

Loss at smoke-stack 2,316 " 16.5 " 

Ash and waste 764 " 5-5 " 

14,000 B. T. U. 100 per cent. 

and concludes that combustion in the furnace of the locomotive 
may be, and often is, practically perfect, and anticipates that 
economy in the formation of steam will only be improved by 
utilizing heat now wasted at the chimney. The usual maxi- 
mum evaporation is about 8 times the weight of coke used 
— a low figure, which is mainly due to the comparatively small 
proportion of heating-surface adopted. The nearer the compo- 
sition of the fuel approaches that of coke, the better, as a rule, 
the economical effect. Coal gives, as an average, about two 
thirds the effect of coke, as customarily burned ; and its value 
may be fairly approximated, the composition being known, by 
assuming the carbon to be the only useful constituent. 



ORDINARY CALORIFIC VALUES AS COMPARED WITH GOOD BITUMINOUS 

COAL. 

Lbs. Coal. 

I cord (3 .62 cubic metres) of seasoned hickory or hard maple 2,000 

I " " " " white oak i,750 

I " " " " beech, red or black oak 1,500 

I " ** *' " poplar, chestnut, or elm. .. , 1,000 

I ** " " " soft pine 960 

85. Analyses of Ash. — The following analyses represent 
the character of ashes of anthracite and bituminous coals. 

They may be taken as examples simply, since the ash of 
coal intended for metallurgical purposes should invariably be 
examined before taking the fuel for any important work. 

ANALYSES OF ASH. 





Specific 
Gravity. 


Color 
of Ash. 


Silica. 


Alum- 
ina. 


Oxide 
Iron. 


Lime. 


Mag- 
nesia. 


Loss. 


Acids 
S.&P. 


Pennsylvania Anthracite 

" Bituminous 

Welch Anthracite 


1-372 
1.32 
1.26 
1.27 


Reddish 
Buff. 
Gray. 


45.6 
76.0 
40.0 
37-6 
19-3 


42.75 

21.00 

44-8 

52.0 

H.6 


9-43 
2.60 


1. 41 

12.0 

3-7 

23-7 


0-33 

trace 
I.I 
2.6 


0.48 
0.40 


2.97 
5.02 
33-8 




Li&rnite 





* Railway Machinery, p. 122. 



THE FUELS. AND THEIR COMBUSTION. 20I 

Where the difference between two coals lies principally in 
their relative percentages of ash, the comparison is made in the 
manner about to be described. 

The anthracites contain so little other combustible matter, 
th'at, as shown by Professor Johnson,^ their calorific value is 
proportional very nearly to the percentage of contained carbon. 

86. The Commercial Value of Fuels is somewhat modi- 
fied by the depreciation produced by presence of non-combus- 
tible matter ; this modification occurs in the following ways : 

(i) A certain amount of carbon is required to heat the 
whole mass to the temperature of the furnace. Of this a large 
part is lost. It follows, therefore, that a coal containing a cer- 
tain small quantity of combustible would have no calorific value, 
and consequently would be worthless in the market. 

(2) The presence of a high percentage of ash in a fuel 
checks combustion by its mechanical mixture with the com- 
bustible portion of the coal. A coal will, hence, have no com- 
mercial value when the proportion of refuse reaches a limit at 
which combustion becomes impossible in consequence of this 
action. 

(3) The cost of transportation of ash being as great as that 
of transporting the combustible, the consumer paying for ash 
at the same rate as for the carbon, and also being compelled to 
go to additional expense for the removal of ash ; these facts 
also determine a limit beyond which an increased proportion of 
ash renders the fuel valueless. 

(4) The determination of the financial losses due to in- 
creased wear and tear of furnaces and boilers, of incidental 
losses due to inequality or insufficiency of heat-supply, and to 
the many other direct and indirect charges to be made against 
a poor fuel, also indicate a limit which has a different value for 
each case, but which, in most cases, is difficult of even approxi- 
mate determination. The determination of the minimum pro- 
portion of combustible, under the first case, is made as follows, 
assuming this heat to be entirely wasted : 

{a) The specific heat of ash is usually nearly 0.20. Let X 



* Report to the Navy Department on American Coals. 



202 THE STEAM-BOILER. 

represent the percentage of ash which is sufficient to render the 
coal valueless. Then, since each pound of carbon has a heat- 
ing-power of 14,500 British thermal units (3625 calories), 14,500 
(100 — Jr) = -^, represents the available heat of a unit in 
weight of the fuel ; 100 X 0.20 X 3000° = j5, represents the 
heat required to raise this same amount of coal to a temperature 
equal to that of the furnace, which is here assumed at 3000^ 
Fahr. (1633° Cent.) above the surrounding atmosphere. 

Since these quantities'^ and B are equal : 14,500 (100 — Jf) 
= 100 X 0.2 X 3000°, and X — 96 per cent. 

The minimum quantity of fuel permissible is, therefore, 
four per cent, where the first consideration only is taken into 
the account. 

iU) The influence of the second condition is at present not 
determinable in the absence of experiment. 

{c) The cost of transportation of ash to the consumer, as a 
part of the fuel, is not taken in the determination of its value 
to him. The removal of ash is a tax upon the consumer which 
may be considered as the equivalent of the loss of a certain 
weight of combustible received. Since this cost fluctuates with 
the market value of coal, and since its amount is determined by 
the same causes, it is easy to make the statement in that form. 
This cost is about ten per cent of the value of coal, weight for 
weight, and is therefore assumed at ten per cent of the propor- 
tion of ash found in the coal. 

(d) The losses, direct and indirect, coming under the fourth 
head, vary greatly, and are sometimes very serious. An ap- 
proximate estimate for an average example is taken, and is 
considered to be equal, at least, to a percentage of the total 
value of coal, in utilizable carbon, which equals one half the 
percentage of ash. Comparing two anthracites, which we will 
suppose to contain, respectively, fifteen and twenty-five per 
cent ash, eighty-five and seventy-five per cent carbon, the first 
being a well-known standard coal, selling in the market at six 
dollars per ton (ici6 kilogrammes), we may, using this system 
of charging losses against equivalent values in combustible car- 
bon, determine the proper commercial value of the second 
kind. 



THE FUELS AND THEIR COMBUSTIONS 203 

First Example. — From the 85 per cent carbon : 

Deduct for heating to furnace temperature 0.040 

•' " transportation of refuse 10 per cent of 15 0.015 

•* " other losses 50 per cent of 15 0.075 

Total 0.130 

leaving valuable and available carbon 85 — 13 = 72 per cent. 
Second Example. — From the 75 per cent carbon : 

Deduct for heating to furnace temperature 0.040 

" " removal of ash 10 per cent of 25 0.025 

•• " sundry losses 50 per cent of 25 0.125 

Total 0.190 

leaving valuable available carbon 75 — 19 =: 56 per cent. 

Finally, if $6.00 is paid for 72 per cent available combustible, 

for 56 per cent we should pay — — $4.66f . 

72 

Third Example. — Taking a third example, in which the fuel 
contains the exceptionally large proportion of 30 per cent ash, 
we should, by similar method, proceed as follows, deducting 
from the seventy per cent carbon as before the estimated 
charges against it : 

Deduct for heating 0.040 

" " removal of ash 10 per cent of 30. 0.030 

** *' sundry expenses 50 per cent of 30 o. 150 

Total 0.220 

leaving available carbon, 70 — 22 = 48 per cent, which would 

, 48 X 6 
be worth = $4.00. 

Had the first coal had a market value of seven dollars per 
ton, the second and third would have been worth, respectively, 
$5,444 and S4.66I. 

Expressing this operation by symbols, if V represents the 
value of the fuel in percentage of pure carbon, and-^ equal the 
percentage of ash, F = 0.96 — 1.60A. 

This method is evidently largely empirical, and its results 



204 THE STEAM-BOILER. 

arc but approximate. It is, however, simple and easily applied, 
and will often be found of use in the absence of more precise 
means of determination. 

The kind and quality of fuel employed in the production of 
steam for commercial purposes is often determined by condi- 
tions quite independent of the special quality of the fuel. In 
most cases the element of cost is the controlling one. 

Johnson, in his report to the Navy Department (1844) on 
American coals, proposes to grade coals according to — 
i) Their relative weights. 

'2) Rapidity of ignition. 

'3) Completeness of combustion. 

^4) Evaporative power under equal weights. 

'5) Evaporative power under equal bulks. 

^6) Evaporative power of combustible matter. 

j) Freedom from waste in burning. 

^8) Freedom from tendency to form clinker. 

^9) Maximum evaporative power under equal bulks. 
10) Maximum rapidity of combustion. 

He found it impossible to select any one coal which could 
be placed first in all these qualities or to attach equal impor- 
tance to all. For steam navigation he attaches most impor- 
tance to the fifth, " the evaporative power for equal bulks," as 
stowage-space is supremely important in steam navigation. 
With the fifth he combines the eighth and tenth, viz., " free- 
dom from clinker" and '' maximum rapidity of action." Ameri- 
can coals are usually superior to foreign coals. 

87. Good Furnace Management, to secure maximum 
heat-supply from the unit weight of fuel, is evidently as essen- 
tial to economy and efificiency of steam production as choice of 
proper fuels. 

In the management of the furnace the effort should be 
made to secure the best conditions for economy, and as nearly 
as possible perfect uniformity of those conditions. The fuel 
should be spread over the grate very evenly, and the tendency 
to burn irregularly, and especially into holes or thin spots, 
should be met by skilful '' firing," or *' stoking" as it is also 
termed, at such intervals as may by experience be found best. 



THE FUELS AND THEIR COMBUSTION. 20$ 

The smaller the coal, where anthracite is used, the thinner 
should be the fire ; the stronger the draught the thicker the 
bed of fuel, of whatever kind. With too thin a fire, the dan- 
ger arises of excess of air-supply ; with too heavy a fire, carbon 
monoxide (carbonic oxide) may be produced. In the former 
case combustion will be complete, but the heat generated will 
be distributed throughout the diluting excess of air, and thus 
rendered less available, and the efficiency of the furnace will be 
correspondingly reduced ; while in the latter case a loss arises 
from incomplete combustion, and waste takes place by the 
passage of combustible gas up the chimney. The second is the 
less common cause of loss of the two, but both are liable to 
arise in almost any boiler, and we may even have both losses 
exhibited in the same boiler and at the same time. Successful 
working demands a very perfect mixture of the combustible 
with the supporter of combustion, and should this not be 
secured, serious waste will take place. 

The appearance of smoke at the chimney-top is not always 
indicative of serious loss, nor is its non-appearance always proof 
of complete combustion. With soft coals and other fuels con- 
taining the hydrocarbons some smoke usually accompanies 
the best practically attainable conditions ; anthracites, charcoal, 
and coke never produce true smoke. Attempts to improve 
the efficiency of a heat-generating apparatus by " burning the 
smoke" usually fail by introducing such an excess of air as to 
cause a loss exceeding that before experienced from the forma- 
tion of smoke. Thorough intermixture of a minimum air-supply 
with the gases distilled from the fuel is the only means of at- 
taining high efficiency. 

In firing, or stoking, especial care should be taken to see 
that the sides and corners of the grate are properly attended 
to. Regulation of the fire is best secured by the careful ad- 
justment of the damper. The manipulation of the furnace 
doors for this purpose is likely to cause waste. Liquid fuels 
are especially liable to waste by excessive air-supply, and gas- 
eous fuel exhibits a peculiar liability to the opposite method 
of loss ; both should be, if possible, even more carefully handled 
than any solid fuels. 



206 THE STEAM-BOILER. 

88. The Fuels, Boiler, and Furnace must be adapted 
each to the others very carefully, if the best results are to be 
attained. Soft, free-burning fuels demand a different form of 
grate, as well as different air-distribution and furnace manage- 
ment, from the hard and slow-burning combustibles. The 
form and size of furnace, the extent and kind of heating-sur- 
face, and the type of boiler even, all influence the total effi- 
ciency of steam generation. Tubular boilers have small flues or 
tubes, and are better fitted for use with anthracite coal and 
with coke or other fuels burning with little flame ; while larger 
tubes or flues are better adapted for use with the bituminous 
and other soft, long-flaming combustibles. It thus happens, for 
example, that a locomotive using anthracite coal, another en- 
gine burning bituminous coal, and a coke-burning engine, all 
have different proportions of boiler. 



CHAPTER IV. 

HEAT — PRODUCTION ; MEASUREMENT ; TRANSFER ; EFFICIENCY 
OF HEATING-SURFACE. 

89. The Nature of Heat, long debated among men of 
science, has in the course of the last century become well 
determined. Heat consists in the vibrations of the molecules 
of which bodies are composed, and is a form of energy. This 
energy, although actually kinetic, being molecular is often 
taken to be potential or latent. The two forms in which 
energy is stored, when heat is communicated to any substance, 
are " sensible heat," of which the intensity is exhibited by the 
thermometer, and which is measured in quantity by the 
various methods of calorimetry ; and '' latent heat," which is 
not detected or measurable as heat, and which in fact does not 
exist as heat, but has been transformed into the true potential 
energy of changed physical state and altered molecular rela- 
tions : it is manifested by a change of volume in the body 
affected. 

Thus all masses, of whatever kind, composition, or form, 
when heated increase in temperature and are altered in vol- 
ume, and the sum of the heat-energy producing the change in 
temperature and the potential energy measured by the prod- 
uct of the change of volume and the total intensity of the 
forces, internal and external, resisting that change measures 
the total heat transferred to effect the physical changes noted. 
The sensible heat retains its original form ; the latent heat, so- 
called, is no longer heat at all, but may be retransformed and 
may again appear as heat on reversing the first operation of 
transfer. In solids, by far the greater part of the heat received 
remains sensible, and takes effect in producing change of tem- 
perature ; in the transformation of the solid into liquid by 
fusion all heat absorbed becomes latent, and produces ex- 



208 THE STEAM-BOILER. 

pansion of volume ; in heating the liquid the heat is employed 
mainly in elevation of temperature, but in part in doing work 
with the result of transformation into latent heat. During 
vaporization at any fixed temperature all heat is disposed of 
in causing change of volume, and this is known as the " latent 
heat of evaporation," or of vaporization ; while in the expan- 
sion of vapors and gases the increase of volume continues to 
be comparatively large in amount, and the *' latent heat of ex- 
pansion" is a correspondingly large proportion of the total, 
and is especially large in vapors, such as steam, which have 
great internal potential energy due to the action of powerful 
molecular attractive forces. The heat-energy demanded to 
make steam in the boiler is thus, at ordinary temperatures, ten 
times greater than that required to overcome the external 
pressure measured by the steam-gauge. 

90. Production of Heat by Combiistion and other meth- 
ods involves, in all cases, the expenditure of an equivalent 
amount of energy in some transformable shape. 

The original source of all heat-energy is found far back of 
its first appearance in the steam-boiler. It had its origin at 
the beginning, when all Nature came into existence. After 
the solar system had been formed from the nebulous chaos of 
creation, the glowing mass which is now called the sun was the 
depository of a vast store of heat-energy, which was thence 
radiated into space and showered upon the attendant worlds 
in inconceivable quantity and with unmeasured intensity. 
During the past life of the globe the heat-energy received 
from the sun upon the earth's surface was partly expended in 
the production of great forests, and the storage, in the trunks, 
branches, and leaves of the trees of which they were composed,, 
of an immense quantity of carbon, which had previously ex- 
isted in the atmosphere, combined with oxygen, as carbonic 
acid. The great geological changes which buried these forests 
under superincumbent strata of rock and earth resulted in the 
formation of coal-beds, and the storage, during many succeed- 
ing ages, of a vast amount of carbon, of which the affinity for 
oxygen remained unsatisfied until finally uncovered by the 
hand of man Thus we owe to the heat and light of the sun> 



HEAT— PRODUCTION; MEASUREMENT; TRANSFER. 209 

as was pointed out by George Stephenson, the incalculable 
store of potential energy upon which the human race is so 
dependent for life and all its necessaries, comforts, and lux- 
uries. 

■ This coal, thrown upon the grate in the steam-boiler, takes 
fire, and, uniting again with the oxygen, sets free heat in pre- 
cisely the same quantity that it was received from the sun and 
appropriated during the growth of the tree. The actual energy 
thus rendered available is transferred, by conduction and radia- 
tion, to the water in the steam-boiler, converts it into steam, and 
its mechanical effect is seen in the expansion of the liquid into 
vapor against the superincumbent pressure. Transferred from 
the boiler to the engine, the steam is there permitted to ex- 
pand, doing work, and the heat-energy with which it is charged 
becomes partly converted into mechanical energy, and is ap- 
plied to useful work in the mill or to driving the locomotive or 
the steamboat. 

Thus we trace the store of energy received from the sun 
and contained in the fuel through its several changes until it is 
finally set at work ; and we might go still further and observe 
how, in each case, it is again usually retransformed and again 
set free as heat-energy. 

The transformation which takes place in the furnace is a 
chemical change ; the transfer of heat to the water and the 
subsequent phenomena accompanying its passage through the 
engine are physical changes, some of which require for their 
investigation abstruse mathematical operations. A thorough 
comprehension of the principles governing the operation of the 
steam-boiler can only be attained after studying the phenom- 
ena of physical science with sufficient minuteness and ac- 
curacy to be able to express with precision the laws of which 
those sciences are constituted. The study of the philosophy 
of the generation and application of steam involves the study 
of chemistry and physics, and of the new science of energetics, 
of which the now well-grown science of thermo-dynamics is a 
branch. 

These sciences, like the steam-engine itself, have an origin 
which antedates the commencement of the Christian era ; but 
14 



2IO THE STEAM-BOILER. 

they grew with an almost imperceptible growth for many cen- 
turies, and finally, only a century ago, started onward suddenly 
and rapidly, and their progress has never since been checked. 
They are now fully-developed and well-established systems of 
natural philosophy. Their consideration is the special province 
of works on the physical sciences and on applied mechanics. 

Combustion is simply the union of some combustible with 
oxygen ; but this phenomenon involves both chemical and 
physical operations. The first operation is a physical phenom- 
enon : it consists in the elevation of the temperature of one 
or both constituents of the compound to be formed, until, by 
some as yet not clearly understood modification of their mo- 
lecular relations, their chemical affinities come into play and 
combination takes place. But this combination consists in the 
enforced approximation of molecule to molecule, a relative 
motion taking place of great rapidity, and work is thus done 
of considerable amount. The resulting collision converts this 
energy of molecular motion into that energy of molecular 
vibration familiar to us as heat, and the quantity of heat so 
produced is the measure of the potential energy of chemical 
affinity in which it has its origin. With its development in 
this form this energy assumes an available and manageable 
form, and becomes at once capable of application to the pur- 
poses of the engineer. It may now be measured, stored, trans- 
ferred wherever wanted, and finally, as required, transformed 
into mechanical energy, and in that form apphed to all kinds 
of useful work. 

91. Temperatures and Quantities of Heat are related to 
each other as are pressures and work in dynamics. The one is 
a factor of the other, but the first is not a measure of the 
second. Temperature measures the intensity of molecular 
heat-vibrations and the tendency of heat-energy to transfer it- 
self to another body, very much as the pressure or tension of 
a confined gas or of steam measures the tendency to expand. 
In fact, the pressure of a confined gas and the total internal 
and external pressure of a vapor or other substance are directly 
and precisely proportional to the temperature, measured from 
the absolute zero of heat-motion. 



HEAT— PRODUCTION; MEASUREMENT; TRANSFER. 211 

Quantity of heat is the measure of the energy, whether in 
heat-units or in equivalent mechanical units, — thermal units, 
calories, or foot-pounds, — of the heat transferred in any change. 
It is equal to the product of the weight of the mass affected, 
its specific heat and the range of temperature marking the 
change. 

Temperatures are measured in either Fahrenheit or centi- 
grade degrees, and on either the common or the absolute scale. 
On the Fahrenheit thermometric scale the range of tempera- 
ture between the two standards, the melting-point of ice or the 
freezing-point of water, under normal atmosphere and pressure, 
and the boiling-point of pure water under one atmosphere, is 
divided into 1 80 equal parts or degrees, and the zero is con- 
ventionally placed thirty-two degrees below the former point, 
the freezing and boiling points thus being found at 32° Fahr. 
and 212° Fahr., respectively. On the centigrade thermometer 
the range between the standard temperatures is made 100°, and 
the zero is taken conventionally at the lower of these two tem- 
peratures, the freezing and boiling points being thus at 0° Cent, 
and 100° Cent., respectively. 

The " absolute scale" of temperatures is one on which it is 
sought to place the zero-point at the absolute zero of heat" 
motion — at that point at which all heat-energy becomes zero and 
temperature ceases to have existence. This is found to be at 
very nearly — 461°. 2 Fahr., or — 274° Cent. ; so that, on the ab- 
solute scale, the standard temperatures are -|- 393°. 2 Fahr. and 
-|- 5 73°. 2 Fahr., or -f 274° Cent, and -[- 374° Cent. It is found 
that the scale of the air-thermometer is sensibly coincident 
with the absolute scale, provided its readings are made propor- 
tional to the volumes of the enclosed gas at the several tem 
peratures. Calling T the temperature on this scale the charac 

pv 
teristic equation -^ = constant is found correct for all true 

gases, / and z> being the pressure and volume of unity of 
weight at any assumed temperature, T; hence for the air-ther- 
mometer, in which/ is constant, v cc T. 

The Thermal Unit, the unit by which quantity of heat is 
measured as heat, is that amuunt of heat-energy which is de- 



212 THE STEAM-BOILER. 

manded to raise the temperature of unity of weight of water 
from the temperature of maximum density to one degree 
above that point. The British thermal unit is measured, cus- 
tomarily, by the engineer, by the ''pound-degrees," and quanti- 
ties of heat are measured by the number of such thermal units 
transferred. The metric thermal unit or " calorie," as it was 
called by the French philosophers who first adopted the metric 
system, is that quantity of heat which is required to raise the 
temperature of one kilogramme of water one degree centi- 
grade, — the " kilogramme-degree." 

Specific Heat is the quantity of heat in thermal units de- 
manded by unity of weight of any given material, as of water 
to raise its temperature one degree. When this heat is all 
sensible, it is simply called specific heat, but when it is in any 
observable amount latent, as in expansion of gases, a distinction 
must be made between the '' Specific Heat at Constant Vol- 
ume," which is the real specific heat, and the '' Specific Heat 
at Constant Pressure," and other specific heats involving more 
or less transformation of heat in the performance of the work 
of expansion. The specific heats of the gases are given in § 78 
for constant pressure. Those of the solids are given in the 
following table : 



SPECIFIC HEATS OF METALS AND MINERALS. 

Iron 0.1 1379 ace. to Regnault, o.iioo ace. to Dulong and Petit. 

Zinc 0.09555 " " 0.0927 

Copper 0.09515 ** " 0.0949 " ** ** 

Brass 0.09391 " " 

Silver 0.05701 " " 0.0557 " " 

Lead 0.03140 ** " 0.0293 ** ** '* 

Bismuth 0.03084 " " 0.0288 "■ ** 

Antimony 0.05077 " " 0.0507 " " " 

Tin 0.05623 " *' 0.0514 '• '* •* 

Platinum 0.03243 '* ** 0.0314 " " " 

Gold 0.03244 •• " 0.0298 *• ** ** 

Sulphur 0.20259 " " 0.1880 ** " " 

Coal 0.24111 " " 

Coke 0.20307 ** ** 

Graphite 0.20187 " " 

Marble 0.20989 " ** 



HEAT— PRODUCTION; MEASUREMENT; TRANSFER. 

Unslaked Lime. 0.2169 according to Lavoisier and Laplace. 

Oak-wood 0.570 " "Mayer. 

Glass 0.19768 " " Regnault. 

Mercury 0.03332 " " " 



213 



Laplace and Lavoisier employed the method by melting ; 
Dulong and Petit, the cooling method ; Pouillet, and recently 
also Regnault, the method by mixture, which seems to be the 
most accurate method. 

Coke, coal, masonry, and the stones and earths may be taken 
as averaging very closely c = 0.20. The woods range from 
^ = 0.50 to ^ == 0.65. 

The specific heat of the same material, as has been seen, 
is not perfectly constant, but increases as the temperature in- 
creases. Thus, according to Dulong and Petit, the mean spe- 
cific heat is as follows : 



Iron between 0° and 100° 

Mercury " " " 

Zinc " 

Copper ** ** " 

Platinum 

Glass * ** " 



0.1098; between 0° and 300°, 0.1218 
0,0330; " " " 0.0350 

0.0927; " " " 0.1015 

0.0947; '* " " 0.1013 

0.0335; " ** •' o 0355 

0.1770; " ** •' 0.190 



Regnault found the ratio of the specific heats of the gases 
to be : 



Air 

Hydrogen 

Nitrogen 

Carbonic Acid. . 
Carbonic Oxide. 
Nitrous Oxide . 

Cyanogen 

Sulphurous Acid 



Constant 


Volume, 


1.3665 




3667 




3668 




3688 




3667 




3676 




3829 




3843 



Constant 
Pressure. 



1.3670 
1.3661 

1.3669 
1-3719 
I. 3719 

1.3877 
1.3903 



A relation between the specific heat and the atomic weight 
originally established by Dulong and Petit, and confirmed by 
E-egnault, is very interesting. The product of the specific 



At. Wts. 


Products. 


339-21 


38.597 


675.80 


38.527 


1233.5 


39-993 


201.17 


40.754 



214 THE STEAM-BOILER. 

heats and the atomic weights is nearly constant, and varies only 
from 38 to 42 ; thus : 

c. 

For Iron 0.11379 

" Silver 0.05701 

' ' Platinum o. 03243 

" Sulphur 0.20259 

92. Thermometry and Calorimetry are the processes em- 
ployed by physicists and engineers in the quantitative deter- 
mination of temperatures, and of quantities of heat and their 
variations. The instruments employed consist of the various 
kinds of thermometers and pyrometers for measuring tempera- 
tures, and of several sorts of calorimeter, the form being deter- 
mined by the character and accuracy demanded by the work 
to be done. 

Thermometers usually consist of a bulb, commonly of glass, 
and a capillary stem which the fluid inclosed traverses as its 
volume changes, the position of the head of the column at 
any moment indicating the temperature attained by the instru- 
ment at the instant, the reading being taken from a scale 
established by the maker and standardized by reference to the 
standard temperatures or by comparison with another instru- 
ment of known accuracy. 

Mercury is generally used in thermometers ranging from 
below the freezing-point up to about 500° Fahr. (260° Cent.). 
For the extremely low temperatures at which mercury might 
freeze, alcohol is used, and it may be employed also for familiar 
atmospheric temperatures. For temperatures approaching or 
exceeding the boiling-point of mercury, the various metallic 
thermometers or '* pyrometers" are used, which depend for 
their operation upon differences in the rates of expansion of 
two metals. Siemens' electric pyrometer depends for its action 
on the variation of the resistance of a conductor of electricity 
with variation of temperature. 

The finer kinds of thermometer used in the thermometry 
of the engineer are mainly employed in the determination of 
temperatures of air and water, in the measurements connected 



HEAT— PRODUCTION; MEASUREMENT; TRANSFER. 21 5 

with steam-boiler trials. They are always mercurial thermom- 
eters, and are made and standardized with the utmost possible 
accuracy ; those used in the calorimeters employed in deter- 
mining the character of the steam furnished by boilers are often 
graduated to tenths, or even to twentieths, of degrees. The 
pyrometers used by the engineer are commonly constructed of 
a tube inclosing a rod of a different metal, the two secured 
together at one end, while at the other end the tube carries a 
case and dial, and the rod actuates a pointer, through some 
system of multiplying gear. The tube is usually of iron, and 
the rod of brass or copper. A more sensitive form is that in 
which the disposition of the two metals is reversed. The 
special forms of calorimeter used in connection with boiler 
tests will be described later. 

Regnault's and Wiedemann's experiments, made on simple 
gases, and on carbonic oxide which is formed without con- 
densation, proved that in these cases the specific heat between 
0° and 200° C. is constant ; whilst their experiments on gases 
formed with condensation show that the specific heat varies, 
the mean being given in the following empirical formulae : 

For CO2 = 44 gr. C. = 8.41 -f- 0.0053/) Mean of Regnault 
•' NO =44 " = 8.96 4- 0.0028/ f and Wiedemann. 
** C2S4 =76 " = 10.62 -|- 0.007/, Regnault. 
** NH3 =17 " = 8.51 -f- 0.00265/, Wiedemann. 
" C4H4 = 28 " = 9.42 -|- 0.0115/, Wiedemann. 

93. The Transfer of Heat from the furnace to the boiler 
involves the application of chemical and physical principles 
which will be briefly stated in a succeeding part of this chapter. 
The production of heat by the chemical processes involved in 
construction has been seen to be governed by the nature of the 
fuel, by the relative proportion of combustible and of sup- 
porter of combustion, and by the quantity of diluting gases 
present. The heat, once produced, is the more completely 
available as the temperature of the products of combustion is 
higher ; it is the more completely utilized, also, as the arrange- 
ments for its transfer are the more complete and effective. 

The utilization and the waste of heat are dependent upon 



2l6 THE STEAM-BOILER. 

the method and extent of its transfer to the absorbing appara- 
tus, or to other bodies. The heat generated in the furnace of 
a steam-boiler is usually mainly transferred to the boiler by 
radiation, conduction, and convection, partly, often in some- 
what large proportion, to the chimney and the outer air by 
convection, and to some extent to adjacent objects by conduc- 
tion or radiation through the furnace-walls and the occasionally 
opened furnace-doors. The laws and the extent of these utili- 
zations or wastes are fairly well understood, and can be some- 
times calculated with a satisfactory degree of accuracy and 
certainty. 

The tendency to transfer heat by either of the three meth- 
ods, radiation, conduction, or convection, and the quantity so 
transferred, depend upon — 

(i) The difference of temperature between the source and 
the receiver of that heat. 

(2) The extent and character of the surfaces between which 
such transfer takes place. 

(3) The extent and nature of the intervening body or 
bodies. 

It is usually assumed that it is sensibly correct to take the 
quantity transferred, in any case, as measured by the product 
of the difference of temperature by a coefficient obtained for 
each substance by experiment. 

94. Radiation of Heat is the direct transfer of that form 
of energy from one body to another across intervening space, 
the only medium of transfer being the " luminiferous ether," 
the waves in which act as the vehicles of transportation, travel- 
ling at the rate of 186,860 miles (300,574,000 rq.) per second. 
The vibrations of dark, pure heat-waves occur at the rate of 
400,000,000,000,000 per second or less ; those of greater fre- 
quency, up to about double this rate, are light-waves ; and still 
more rapid vibration constitutes the actinic or chemical ray. 
The slowest heat-rays have about one fourth the rate of the 
fastest ; and the most rapid of known actinic rays vibrate one 
hundred times as rapidly as these last. Visibly hot bodies 
emit all kinds of rays. All bodies are continually receiving 



HEAT— PRODUCTION; MEASUREMENT,; TRANSFER. 21/ 

and emitting heat-rays, and, according to Prevost's theory of 
exchanges, gain or lose in total heat and in temperature accord- 
ingly as they gain by absorption from surrounding bodies more 
than they yield to the latter, or the reverse. 

* A good radiator is always a good absorbent. Any body 
which absorbs a particular kind of ray will, when emitting 
energy, radiate the same form. Diathermous substances per- 
mit the heat-rays to pass through, as transparent substances 
admit light-rays : but diathermous bodies are not necessarily 
equally, even if at all, transparent ; and all substances are more 
diathermous to some rays than to others, while good absorbents 
are not diathermous. 

Radiation plays an important part in the operation of the 
steam-boiler, in the furnace of which, when the fire is bright, it 
is estimated that usually about one half of all the heat taken 
up by the generator is received direct from the fuel by radi- 
ation. 

95. Conduction is the method of transfer of heat by flow 
from part to part in the same body, or from one to another of 
bodies in contact. These two phenomena are not precisely the 
same. The flow of heat from a hot to a cold body in contact 
depends not only upon the conducting power of the two sub- 
stances, but also, and often mainly, on the condition of the 
touching surfaces and the perfection of their contact. The rate 
of transfer within any given material depends solely on the 
variation of temperature along the line of flow, and on the 
character of the substance. 

Conductivity measures the rate of flow, or of transfer of 
heat, under any assumed and defined conditions ; it is the 
power of transmission of heat. The rate of conduction, or the 
conductivity, may be expressed by the number of thermal 
units passing across a surface, or through an internal section, 
in the unit of time ; it is proportional to the rate of variation 
of temperature along the line of flow and to the constant co- 
efificient denominated the conductivity, or the coefficient of con- 
ductivity. Thus the quantity, Q, of heat passing in any given 
time, t, is measured by the product of that time into the con- 



2l8 THE STEAM-BOILER. 

ductivity, k, and into , , the rate of variation of temperature 
with distance traversed, and area of section, A^ 



The value of k varies greatly with different substances, be- 
ing comparatively high with the metals and very low with all 
organic materials and the minerals. Where k is constant, the 
equation above given becomes 

T — T 
Q = Akt-^ — ^. ...... (2) 



Where, as is often the case, the thermal resistance instead 
of the conductivity is taken, we shall have, when r is the co- 
efficient of resistance, ^ = j, and 

e = ^-#^'. (3) 

and the following values of r are found by experiment, accord- 
ing to Peclet, for x in inches and Q in British thermal units 
per hour :^ 

Gold and silver 0.0016 

Copper 0.0018 

Iron , 0.0043 

Zinc • , 0.0045 

Lead 0.0090 

Stone 0.0716 

Brick 0.1500 

Where the plate consists of laminae, each may be considered 
by itself, and the total resistance obtained by adding together 
the resistances of the several parts. 

* Vide Rankine's Steam-engine, p. 259. 



HEAT— PRODUCTION; MEASUREMENT; TRANSFER. 219 

The surface resistance forms so large a part of the total in 
steam-boiler practice, that the formula 



Q = ^I^^^ (4) 



may be conveniently used to compute the amount of heat 
transferred, a being taken as from 150 to 200 in British meas- 
ures (15 to 20 in metric measures), accordingly as the surfaces 
are clean or not, the plate being of iron, with water on one side 
and hot gases on the other. 

96. Convection of Heat occurs by its communication to 
the particles of a fluid, and then by the flow of those particles 
into new positions, and by their contact with the receiver of 
heat by the transfer of that heat to such receiver. Convection 
is the only method of transfer in liquids, since conductivity is 
not appreciable, and it is only by its transportation by means 
of currents that it can be transferred at all. A good circulation 
is therefore essential to rapid transfer, and the rate of transfer 
is thus in a sense proportional to the efficiency of circulation. 
Thus the efficiency of a steam-boiler is dependent upon the 
effectiveness of its circulation, as well as upon the extent and 
conductivity of its heating-surfaces. A quiescent mass of water 
or of gas is incapable of transferring heat, and that element can 
only pass such a mass by penetrating it as radiated energy, its 
vehicle being the ether, which pervades all diathermic sub- 
stances. Heat applied to the surface of still water does not 
pass downward at all or in any direction by real conduction ; 
applied at one side or at the bottom of the mass, currents are 
at once set up, by means of which a rapid upward transfer of 
heat may take place. Thus convection invariably produces 
transportation of heated particles, and transfer of heat, from 
the source of heat to a receiver of heat, or a refrigerator, at a 
higher level. For best effect the heat must in all cases be 
applied at the lowest part of the fluid mass. These facts and 
deductions are equally true of liquids and gases, the latter 
being even more perfect non-conductors than the former. 



220 THE STEAM-BOILER. 

Condensation of steam and other vapors by contact with 
cooling surfaces at temperatures below those of vaporization 
always occur by a peculiar convection, the circulating or mov- 
ing currents of vapor streaming toward the refrigerating sur- 
faces, these streams having their origin in the condensation of 
the vapor in contact with the latter, and the formation thus of 
a vacuous space into which they are driven by the elasticity of 
the fluid. A continuous condensation and steady flow is pro- 
duced, and is sustained as long as these conditions persist. 
This operation is the most rapid of all known methods of con- 
vection or of transfer of heat, the mobility of the vapor per- 
mitting the most rapid movement of its currents, and its instan- 
taneous condensation preserving a constant head which forces 
the fluid in the direction of the condensing surface on which it 
is converted into a liquid of comparatively small volume and 
capable of prompt and complete removal. 

97. The Transfer of Heat in Boilers is due to convec- 
tion largely. It is obvious that where transfer of heat takes 
place from one fluid to another through the sides of a contain- 
ing vessel, as in the steam-boiler, or the surface-condenser of 
the marine steam-engine, the two fluids should be so circum- 
stanced that their currents should flow in opposite directions, 
the heating or the cooled fluid entering on the heating-surface 
of the boiler or other vessel at its point of maximum tempera- 
ture, and passing off at the coolest part ; while the coo'.ing or 
heated fluid, the receiver of heat, should come into contact 
with the separating sheet of metal at its coldest part and pass 
off at the hottest. In the steam-boiler the feed-water should 
enter at that part at which the furnace-gases are entering the 
chimney-flue, and should circulate toward the furnace. In the 
surface-condenser the condensing water should enter near 
where the water of condensation is taken away by the pumps, 
and should issue near the point at which the steam enters. It 
is further evident that in the latter case, other things being 
equal, that disposition of apparatus which permits most rapid 
and complete removal of the drops and streams of water of 
condensation from the cooling surfaces, so as to give at all 
times the maximum possible area of effective surface, will pro- 



EFFICIENCY OF HEATING-SURFACE. 221 

duce the highest efficiency. This has been found practically of 
essential importance in the design and construction of such 
condensing apparatus. 

Feed-water heaters for the above-stated reasons are placed 
in the chimney-flue, while superheaters are sometimes placed 
in the furnace. Considerations of convenience and economy, 
however, oftener compel the designing engineer to place the 
latter at the exit of the furnace gases from the boiler and 
between the latter and the feed-water heater. As a rule, how- 
ever, the rapidity and completeness of the circulation of the 
waters in a well-designed boiler are such that the point of 
introduction of feed-water is a matter of minor importance, so 
far as the boiler itself is concerned ; and the engineer usually 
seeks to enter the feed in such a manner as shall evade risk of 
injury by irregular strains due to excessive differences of tem- 
perature in its different parts. The mass of water in a good 
boiler, freely steaming, may be assumed to have substantially 
uniform temperature, and only the furnace gases need be con- 
sidered as flowing in definite paths with varying temperature. 
The use of the " counter current, as it is called, is better illus- 
trated practically in the case of the condenser. 

Experience shows that the thickness of the intervening 
plate has practically no important influence, as a rule, on the 
efficiency of transfer. Thick furnace-flues and thin tubes in 
the steam-boiler seem about equally effective ; and the Author 
has known cast-iron condenser-tubes to work practically with 
the same efficiency as the thin brass tubes, of one quarter their 
thickness, customarily employed. It should be stated, how- 
ever, that sheets of iron or steel in the furnaces of boilers, or 
in flues where exposed to nearly furnace temperatures, are 
liable to injury by " burning," if very thick, and especially if 
the laps of their seams are so exposed. In some cases the law 
forbids the use of heavy plates in furnace-flues or parts exposed 
to flame. 

98. Efficiency of Heating or Cooling Surface measures 
the ratio of actual amount of heat transmitted across such sur- 
face to the total quantity available for such application ; in 
steam-boilers it is the ratio of the quantity of heat utilized in 



222 THE STEAM-BOILER. 

heating and vaporizing the fluid to the total which is produced 
by the furnace, the unutiHzed heat being wasted by conduction 
and radiation to other bodies, or sent up the chimney. An 
expression was found by Rankine, based upon equation (4) of 
article 95, which has been found to give very satisfactory re- 
sults when properly used in application to the ordinary work of 
steam-boilers. This expression may be derived as below. 

Let w be the weight of furnace-gases discharged per hour, 
T — t the difference between the temperatures of gas and water 
on opposite sides of any part of the plate on the elementary 
area dS^ C the specific heat of the gas, and let q be the 
quantity of heat passing across unity of area in unity of time 
for a difference in temperature T — /, in other words, the " rate 
of conduction" per unit of area per hour. 

The quantity of heat transferred across the area dS is then 
equal to qdS, and the fall of temperature of gas must be this 
quantity divided by the product of the weight, w, and specific 
heat, C, of the gas from which the heat is derived, 

S = -^^' • • (■) 

and the gas flows on to the next elementary area and beyond, 
surrendering its heat as it goes, until it finally leaves the ab- 
sorbing surface and enters the chimney-flue. 

If T^ and T^ are the initial and final temperatures of the 
gas, and t the temperature of the water entering the boiler, the 
heat produced, g,, and that wasted, Q^, per hour, are respec- 
tively measured by 

Q^ = Cw{T, - /) : a = Cw{T, - t\ nearly; . . (2) 

while the efficiency of the heating-surface is measured by the 
ratio of total heat to absorbed heat ; or, if the feed enters at 
atmospheric temperature, or nearly so, by 

O — T — T 

^^' = l^.nearfy (3) 



EFFICIENCY OF HEATING-SURFACE. 223 

The heat utiHzed, Cw{T^— T^), is also equal to that ab- 
sorbed and transmitted, gdS: 



fgdS=Cw{r,-r,) and ~=^^'^. . . (4) 



The value of ^ has been found to be well represented 
by equation (4) of article 95, in which q = -j-, and hence 

q = ^-^ ^^ ; and thus 



_5 _ r^'d_l_ r'^' dT 

Cw-Jr, q -Vr, {T - tf ^5) 

Assume {T — t) = x, then 

aCw Jt^ (^T-t)''~Jj- ^ ^^ 
. s_ _]_ _r (7-,-/) -(?;-/) 



• • aCw T,-t T,-t- {T,-t){T,-t)' 
and the efficiency becomes 



Then, since 



T,— t aCw aCw ' 



(7) 



T — T S 



224 


THE STEAM-BOILER. 


and 


{T,-t)-{T^-t) T,-T^ 




r.^T,-T, _ S{T,-t) 



T,-t S{T,-t) + aCw ' 
If the total heat absorbed per hour be taken as H^ 



(9) 



H^Cw{T,-t); r,_^ = ^; . . . (10) 
and a simplified expression, 

^+ ^ - 

is obtained, in which Cw may be taken as proportional to the 
weight of air supplied or of fuel burned, and H as proportional 
to the same quantity. Thus if F is the weight of fuel burned 
in the given time, on unity of grate-area, the efficiency may be 
expressed as 

r,__ BS B 

^~ S-\-AF~ \-\- AR' • • • • ^^2) 

which is the formula sought. A and B are constants to be ob- 
tained by experiment for the special type of boiler to be con- 
sidered. 

When 5 and F represent respectively the number of square 
feet of heating-surface per square foot of grate in any boiler, 
and the number of pounds of fuel burned as the square foot of 

F 
grate per hour, and R = -^, the values of A and B, as given by 

Rankine,* are as follows : 

* Steam-engine, p. 294. 



EFFICIENCY OF HEATING-SURFACE. 



225 



Boiler Type. A. 

Class I. Best convection, chimney draught 0.5 

2. Ordinary " " " 0.5 

" 3. .Best " forced " 0.3 

'* 4. Ordinary " " " 0.3 



B. 
1. 00 
0.90 
1 .00 
0.95 



These constants are derived from experience with good 
fast-burning bituminous coals; for anthracites of good quality 
the Author has usually found the following values more in ac- 
cordance with good practice : 

Boiler Type. A. B. 

Class 1 0.5 0.90 

" 2 0.5 0.80 

'• 3 0.3 090 

" 4 0-3 0-85 

When feed-water heaters are used, or superheaters are em- 
ployed, their surface should be included in the area S. The 
formula assumes no loss by excess of air-supply. Where such 
excess is noted or anticipated, it may be allowed for by increas- 
ing the value of A in proportion to the square of the total 
quantity of air supplied. The following table presents values 
of efficiency for a wide range of practice : 

EFFICIENCY OF BOILERS. 







Bituminous Coal. 






Anthracite Coal. 




R. 




Class of Boiler. 






Class of Boiler. 






I. 


II. 


III. 


IV- 


I. 


II. 


III. 


IV. 


10 


0.16 


0.15 


0.25 


0.22 


0.14 


0.14 


0.23 


0.20 


4 


0.33 


0.31 


0.45 


0.43 


0.30 


0.28 


0.40 


0.39 


2 


0.50 


0.46 


0.62 


0.59 


0.45 


0.50 


0.56 


0-53 


I 


0.6b 


0.61 


0.77 


0.73 


0.60 


0.55 


0.70 


0.66 


0.80 


71 


0.65 


81 


0.77 


0.64 


0-59 


0.73 


o.6(> 


0.67 


0.75 


0.69 


83 


0.79 


0.67 


0.63 


0.75 


0.72: 


0.50 


0.80 


0.73 


0.S7 


0.83 


0.72 


0.65 


0.78 


0.75. 


0.40 


0.83 


0.76 


0.S9 


0.85 


0.75 


0.68 


0.80 


0.77 


0.333 


0.86 


0.80 


0.90 


0.86 


0.77 


0.72 


o.Si 


0.7ft 


0.167 


0.93 


0.85 


0.95 


0.90 


0.84 


0.77 


0.86 


0.81 


O.III 


0.95 


0.87 


0.97 


0.92 


0.86 


0.78 


0.S8 


0.83 



These values have been found to agree well with practice 
up to rates of combustion exceeding 50 or 60 pounds per 
15 



226 THE STEAM-BOILER. 

square foot of grate-surface per hour, beyond which point the 
efficiency falls off. But agreement can only be expected where 
the combustion and air-supply are in accordance with the 
assumptions on which the formula is based. 

The problem of the designer of steam-boilers often takes 
the form : Required to determine the area of heating-surface 
needed to secure a stated efficiency. In this case the formula 
above given must be transformed thus : 



E = 



I + AR~ ^ F' 
F 



'+-S 



^=B ' (13) 



B 



^ = F = B~^-'^ 04) 



from which expressions, the efficiency aimed at being given, 
the ratio of heating to grate-surface and the extent of heating- 
surface may be computed. As will be seen later, the question 
to what extent efficiency may be economically carried by ex- 
tending heating-surface is one of the problems arising in de- 
signing boilers. 

T/ie A7'ea of Cooling-siirface demanded to refrigerate liquids, 
or to condense steam or other vapor, is capable of somewhat 
similar calculation. Returning to the primary equations of the 
preceding article, we have 

fqds^cw{T:-T:), (I) 

in which we may take T^ as the measure of the total heat, per 
unit of weight of the steam entering the condenser or refriger- 



EFFICIENCY OF HEATING-SURFACE. 22/ 

ator, and 7"/ the temperature of the water of condensation at 
its exit. As before, 

in which t becomes the temperature of the circulating or cool- 
ing water, while for such small differences of temperature we 
may take q^ C{T — t\ whence 

5 = MCw log, If^-. 

= N\og,f^^; (3) 



in which expression the value of N may be taken, for ordinary 
steam-engine condensers, at about 0.04, rising in exceptional 
case of inefficient apparatus to o.io, and falling in exception- 
ally good examples to o.oi, British units being used. 

M. Havez has found a similar expression to be practically 
correct for heating-surfaces, and asserts that we may take the 
quantity of heat transmitted in either case as decreasing in 
geometrical progression ; while the length of path swept over, 
measured from the origin, increases in arithmetical progres- 
sion.* Mr. Williams and M. Petiet both found, in experi- 
ments on locomotives, that the evaporation diminished about 
one half at each step, metre by metre, or yard by yard, from 
the furnace to the smoke-box end of the tubes. 

The efficiency of the heating-surfaces of boilers has been 
sometimes considerably increased by the expedient of setting 
pins in the plates in such manner that, projecting into the flue 
or furnace on the one side and the water-space on the other, 
they take up heat from the passing gases and conduct it into the 
midst of the water. A pin may be thus made to absorb and 



Revue Industrielle, Mch. , 1874. 



228 THE STEAM-BOILER. 

utilize several times as much heat as could be taken up by the 
section of the sheet occupied by it. Such '' conductor-pins" 
have often been introduced into marine and other boilers, with 
very evident improvement in results. Even corrugating a 
sheet will produce marked advantage in this manner, especially 
where the direction of the currents is across the lines of corru- 
gation. 

99. The Effect of Incrustation, and of deposits of various 
kinds, is to enormously reduce the conducting power of heat- 
ing-surfaces ; so much so, that the power, as well as the eco- 
nomic efficiency of a boiler, may become very greatly reduced 
below that for which it is rated, and the supply of steam fur- 
nished by it may become wholly inadequate to the require- 
ments of the case. 

It is estimated that a sixteenth of an inch (0.16 cm.) thick- 
ness of hard " scale" on the heating-surface of a boiler will 
cause a waste of nearly one eighth its efficiency, and the waste 
increases as the square of its thickness. The boilers of steam- 
vessels are peculiarly liable to injury from this cause where 
using salt water, and the introduction of the surface-condenser 
has been thus brought about as a remedy. Land boilers are 
subject to incrustation by the carbonate and other salts of lime, 
and by the deposit of sand or mud mechanically suspended in. 
the feed-water. 

It has been estimated that the annual cost of operation of 
locomotives in limestone districts is increased $750 by deposits 
of scale. 



CHAPTER V. 

HEAT AS ENERGY — ENERGETICS AND THERMODYNAMICS. 

100. Heat as a Form of Energy is subject to the general 
laws which govern every form of energy and control all matter 
in motion, whether that motion be molecular or the movement 
of masses. Under the title " Energetics" are comprehended 
all laws affecting bodies, molecules, or atoms in relative motion. 

That heat is the motion of the molecules of bodies was first 
shown by experiment by Benjamin Thompson, Count Rumford, 
then in the service of the Bavarian Government, who in 1798 
presented a paper to the Royal Society of Great Britain, 
describing his work, and reciting the results and his conclusion 
that heat is not substance, but a form of energy. 

This paper is of very great historical interest, as the now 
accepted doctrine of the persistence of energy is a generaliza- 
tion which arose out of a series of investigations, the most im- 
portant of which are those which resulted in the determination 
of the existence of a definite quantivalent relation between 
these two forms of energy and a measurement of its value, now 
Icnown as the " mechanical equivalent of heat." The experi- 
ment consisted in the determination of the quantity of heat 
produced by the boring of a cannon at the arsenal at Munich. 

Rumford, after showing that this heat could not have been 
derived from any of the surrounding objects, or by compression 
of the materials employed or acted upon, says : '' It appears to 
me extremely difficult, if not impossible, to form any distinct 
idea of anything capable of being excited and communicated in 
the manner that heat was excited and communicated in these 
experiments, except it be motion." ^ He estimates the heat 

* This idea was not by any means original with Rumford. Bacon seems to 
have had the same idea; and Locke says, explicitly enough: " Heat is a very 
brisk agitation of the insensible parts of the object, ... so that what in our sen- 
sation is heat, in the object is nothing but motion." 



230 THE STEAM-BOILER. 

produced by a power which he states could easily be exerted 
by one horse, and makes it equal to the " combustion of nine 
wax candles, each three quarters of an inch in diameter," and 
equivalent to the elevation of " 25.68 pounds of ice-cold water" 
to the boiling-point, or 4784.4 heat-units.^ The time was 
stated at '' 150 minutes." Taking the actual power of Rum- 
ford's Bavarian '' one horse" at the most probable figure, 25,000 
pounds raised one foot high per minute, f this gives the 
" mechanical equivalent " of the foot-pound as 783.8 heat-units, 
differing but 1.5 per cent from the now accepted value. 

Had Rumford been able to measure his power and to 
eliminate all losses of heat by evaporation, radiation, and con- 
duction, to which losses he refers, and to measure the power 
exerted with accuracy, the result would have been exact. 
Rumford thus made the experimental discovery of the real 
nature of heat, proving it to be a form of energy, and, publish- 
ing the fact a half-century before the now standard determina- 
tions were made, gave us a very close approximation to the 
value of the heat-equivalent. He also observed that the heat 
generated was '' exactly proportional to the force with which 
the two surfaces are pressed together, and to the rapidity of 
the friction," which is a simple statement of equivalence be- 
tween the quantity of work done, or energy expended, and the 
quantity of heat produced. This was the first great step toward 
the formation of a Science of Thermodynamics. 

Sir Humphry Davy, a little later (1799), published the 
details of an experiment which conclusively confirmed these 
deductions from Rumford's work. He rubbed two pieces of 
ice together, and found that they were melted by the friction 
so produced. He thereupon concluded : '' It is evident that 
ice by friction is converted into water. . . . Friction, conse- 
quently, does not diminish the capacity of bodies for heat." 

* The British heat -unit is the quantity of heat required to heat one pound of 
water 1° Fahr. from the temperature of maximum density. 

\ Rankine gives 25,920 foot-pounds per minute — or 432 per second — for the 
average draught-horse in Great Britain, which is probably too high for Bavaria. 
The engineer's " horse-power" — 33,000 foot-pounds per minute — is far in excess 
of the average power of even a good draught -horse, which latter is sometimes 
taken as two thirds the former. 



HE A T AS ENERG V. 2 3 I 

Bacon and Newton, and Hook and Boyle, seem to have an- 
ticipated — long before Rumford's time — all later philosophers, 
in admitting the probable correctness of that modern dynami- 
cal, or vibratory, theory of heat which considers it a mode of 
motion; but Davy, in 1812, for the first time, stated plainly 
and precisely the real nature of heat, saying: "The immediate 
cause of the phenomenon* of heat, then, is motion, and the laws 
of its communication are precisely the same as the laws of the 
communication of motion." The basis of this opinion was the 
same that had previously been noted by Rumford. 

So much having been determined, it became at once evident 
that the determination of the exact value of the mechanical 
equivalent of heat was simply a matter of experiment ; and 
during the succeeding generation this determination was made, 
with greater or less exactness, by several distinguished men. 
It was also equally evident that the laws governing the new 
science of thermodynamics could be mathematically ex- 
pressed. 

Fourier had, before the date last given, applied mathemati- 
cal analysis in the solution of problems relating to the transfer 
of heat without transformation, and his '' Theorie de la Cha- 
leur" contained an exceedingly beautiful treatment of the sub- 
ject. Sadi Carnot, twelve years later (1824), published his 
" Reflexions sur la Puissance Motrice du Feu," in which he 
made a first attempt to express the principles involved in the 
application of heat to the production of mechanical effect. 
Starting with the axiom that a body which, having passed 
through a series of conditions modifying its temperature, is 
returned to " its primitive physical state as to density, tem- 
perature, and molecular constitution," must contain the same 
quantity of heat which it had contained originally, he shows 
that the efficiency of heat-engines is to be determined by carry- 
ing the working fluid through a complete cycle, beginning and 
ending with the same set of conditions. Carnot was not a 
believer in the vibratory theory of heat,^ and consequently was 
led into some errors ; but, as will be seen hereafter, the idea 

* Documents recently discovered (Comptes Rendus, 1878, p. 967) either show 
this to be an error or prove his later conversion. 



232 THE STEAM-BOILER. 

just expressed is one of the most important details of a theory 
of the steam-engine. 

Seguin, who has already been mentioned as one of the first 
to use the fire-tubular boiler for locomotive engines, published 
in 1839 ^ work, '' Sur I'lnfluence des Chemins de Fer," in which 
he gave the requisite data for a rough determination of the 
value of the mechanical equivalent of heat, although he does 
not himself deduce that value. 

Dr. Mayer of Heilbronn, three yearns later (1842), published 
the results of a very ingenious and quite closely approximate 
calculation of the heat-equivalent, basing his estimate upon the 
work necessary to compress air, and on the specific heats of the 
gas, the idea being that the work of compression is the equiva- 
lent of the heat generated. Seguin had taken the converse 
operation, taking the loss of heat of expanding steam as the 
equivalent of the work done by the steam while expanding. 
The latter also was the first to point out the fact, afterward 
experimentally proved by Hirn, that the fluid exhausted from 
an engine should heat the water of condensation less than 
would the same fluid when originally taken into the engine. 

A Danish engineer, Colding, at about the same time (1843), 
published the results of experiments made to determine the 
same quantity ; but the best and most extended work, and 
that which is now almost universally accepted as standard, was 
done by a British investigator. 

Joule commenced the experimental investigations, seeking 
a measure of the relations of heat and work, which have made 
him famous, at some time previous to 1843, ^-t which date he 
published, in the Philosophical Magazine, his earliest method. 
His first determination gave 770 foot-pounds. During the 
succeeding five orsix years Joule repeated his work, adopting 
a considerable variety of methods, and obtaining very variable 
results. One method was to determine the heat produced by 
forcing air through tubes ; another, and his usual plan, was to 
turn a paddle-wheel by a definite power in a known weight of 
water. He, in 1849, concluded these researches, and announced 
finally the value 772 foot-pounds as that of the mechanical 
equivalent of the British heat-unit. 



HEAT AS ENERGY. 233 

lOl. Energetics treats of modifications of energy under 
the action of forces, and of its transformation from one mode 
of manifestation to another, and from one body to another, 
and within this broader science is comprehended that latest of 
the minor sciences, of which the heat-engines and especially 
the steam-engine illustrate the most important applications — 
Thermodynamics. The science of energetics is simply a wider 
generalization of principles which have been established one at 
a time, and by philosophers widely separated both geographi- 
cally and historically, by both space and time, and which have 
been slowly aggregated to form one after another of the physi- 
cal sciences, and out of which, as we now are beginning to see, 
we are slowly evolving wider generalizations, and thus tending 
toward a condition of scientific knowledge which renders more 
and more probable the truth of Cicero's declaration : '' One 
eternal and immutable law embraces all things and all times." 
At the basis of the whole science of energetics lies a principle 
which was enunciated before Science had a birthplace or a 
name : 

All that exists^ whether matter or force, and in whatever 
form, is indestructible, except by the Infinite Power which has 
created it. 

That matter is indestructible by finite power became ad- 
mitted as soon as the chemists, led by their great teacher La- 
voisier, began to apply the balance, and were thus able to show 
that in all chemical change there occurs only a modification of 
form or of combination of elements, and no loss of matter ever 
takes place. The " persistence" of energy was a later dis- 
covery, consequent largely upon the experimental determina- 
tion of the convertibility of heat-energy into other forms and 
into mechanical work, for which we are indebted to Rumford 
and Davy, and to the determination of the quantivalence 
anticipated by Newton, shown and calculated approximately 
by Colding and Mayer, and measured with great probable 
accuracy by Joule. 

It is now generally understood that all forms of energy are 
mutually convertible with a definite quantivalence ; and it is 
not certain that even vital and mental energy do not fall within 



234 THE STEAM-BOILER. 

the same great generalization. This quantivalence is the basis 
of the science of energetics. 

Experimental investigation and analytical research have 
together thus created a new science, and the philosophy of the 
steam-engine has at last been given a complete and well-defined 
form, enabling the intelligent engineer to comprehend the opera- 
tion of the machine, to perceive the conditions of efficiency, 
and to look forward in a well-settled direction for further ad- 
vances in its improvement and in the increase of its efficiency. 

Energy is the capacity of a moving body to overcome resist- 
ance offered to its motion i"^ it is measured either by the prod- 
uct of the mean resistance into the space through which it is 
overcome, or by the half product of the mass of a free body into 
the square of its velocity. Kinetic energy is the actual energy 
of a moving body ; potential energy is the measure of the work 
which a body is capable of doing under certain conditions 
which, without expending energy, may be made to affect it, as 
by the breaking of a cord by which a weight is suspended, or 
by firing a mass of explosive material. The British measure 
of energy is the foot-pound ; the metric measure is the kilo- 
grammetre. 

Energy, whether kinetic or potential, may be observable 
and due to mass-motion ; or it may be invisible and due to 
molecular movements. The energy of a heavenly body or of 
a coiled spring, and that of heat or of electrical action, are illus- 
trations of the two classes. In Nature we find utilizable poten- 
tial energy in fuel, in food, in any available head of water, and 
in available chemical affinities. We find kinetic energy in the 
motion of the winds and the flow of running water, in the heat- 
motion of the sun's rays, in heat-currents on the earth, and in 
many intermittent movements of bodies acted on by applied 
forces, natural or artificial. The potential energy of fuel and 
of food has already been seen to have been derived, at an 
earlier period, from the kinetic energy of the sun's rays, the 
fuel or the food being thus made a storehouse or reservoir of 



^ The term " energy" was first used by Dr. Young as the equivalent of the 
work of a moving body, in his " Lectures on Natural Philosophy" (1807). 



HEAT AS ENERGY. 235 

energy. It is also seen that the animal system is simply a 
" mechanism of transmission" for energy, and does not create 
but simply diverts it to any desired direction of application. 
. All the available forms of energy can be readily traced back 
to a common origin in the potential energy of a universe of 
nebulous substance (chaos), consisting of infinitely diffused 
matter of immeasurably slight density, whose " energy of posi- 
tion" had been, since the creation, gradually going through a 
process of transformation into the several forms of kinetic and 
potential energy above specified, through intermediate methods 
of action which are usually still in operation, such as the poten- 
tial energy of chemical afifinity, and the kinetic forms of energy 
seen in solar radiation, the rotation of the earth, and the heat 
of its interior. 

The mcasttre of any given quantity of energy, whatever may 
be its form, is the product of the resistance which it is capable 
of overcoming into the space through which it can move 
against that resistance, i.e., by the product RS^ or the equiva- 

WV 
lent expressions and \MV"\ in which W is the weight, M 

the "mass" of matter affected by the motion, Fthe velocity, 
and g the dynamic measure of gravity. 

The three great laws of energetics are : 

(i) The sum total of the energy, active and potential, of the 
universe is invariable. 

(2) The several forms of energy are all interconvertible, and 
possess a definite quantivalence. 

(3) All forms of kinetic energy are tending toward reduc- 
tion to forms of molecular motion and final dissipation through- 
out space. 

102. Heat-energy and Temperature are closely related 
and directly proportional, the one to the other. 

The investigations of physicists have shown that when p 
and V are the pressure and volume of unit weight of any gas, 
and c is the velocity of molecules having the mass m and in 
number n, 

pv = ^7nnc^ \ (i) 



236 THE STEAM-BOILER, 

it is also known that 

pv = RZ (2) 



when R = -7^, the subscripts denoting that these quantities 

o 

are taken at the freezing-point of water, and T is the tempera- 
ture measured from the absolute zero, as hereafter defined 
(— 46i°.2 F., or — 274° C); hence 



Tcxc\ (3) 

and the temperature of any substance, measured on the abso- 
lute scale, is proportional to the kinetic energy of the molecules 
constituting the gas. In other words, as elsewhere stated, 
temperature is a measure of the intensity of molecular vibra- 
tion, while quantity of heat, as has been seen, is quantity of 
molecular energy of vibration. 

Thus temperature, as measured on the absolute scale and 
on the air-thermometer, is directly proportional to the molec- 
ular energy of any given mass, and thus, in the case of any 
confined gas, measures the intensity of pressure on the enclos- 
ing walls due to the heat-energy so imprisoned, which quan- 
tity is also proportional to the product of this pressure into the 
volume of the space throughout which it is exerted. 

103. Quantitative Measures of Heat-energy, obtained by 
the various systems of calorimetry, always involve determina- 
tions of the magnitudes of factors the product of which give 
the quantity of molecular energy present. These factors have 
been seen to be either measures of the mass affected and of 
molecular velocity, or thermal equivalents. The quantity of 
heat-energy to be measured is obtained either by multiplying the 
mass by the square of velocity of vibration, or by the product 
of the weight into the range of temperature considered and the 
mean specific heat : these two measures are equivalent. It 
is by either method made evident that temperature is one 
factor of a product which is the measure of heat-energy, the 



HEAT AS ENERGY. 237 

other factor being a measure of the mass of matter acting as 
the vehicle of that energy. 

104. Heat Transformations may take place, through the 
action of physical and chemical forces, into any other known 
form of energy, and another form of energy may be transmuted 
into heat. Nearly all physical phenomena, in fact, involve 
heat-transformation in one form or another, and in a greater or 
a less degree, under the laws of energetics. According to the 
first of those laws, such changes must always occur by a defi- 
nite quantivalence, and when heat disappears in known quan- 
tity it is always certain that energy of calculable amount will 
appear as its equivalent ; the reverse is as invariably the case 
when heat is produced ; it always represents and measures an 
equivalent amount of mechanical, electrical, chemical, or other 
energy. 

105. Heat and Mechanical Energy are thus evidently 
subject to the general laws of transformation of energy, and the 
transmutation of the one into the other must always be capa- 
ble of treatment mathematically. The relations of these two 
forms of energy are thought by the physicist and the engineer 
as of sufficient importance, and the phenomena involving these 
relations alone are so often found to demand and to permit in- 
dependent consideration, that they are taken as the subject of 
a division of energetics known as the science of thermodynamics, 
and a vast amount of study and research has been given by the 
ablest mathematical physicists of modern times to the investi- 
gation of its laws and their applications, and to the building up 
of that science. 

The conversion of water into steam in the steam-boiler and 
the utilization of the heat-energy thus made available, or in 
heated air and other gases, in steam- or other heat-engines, con- 
stitute at once the most familiar and the most important of 
known illustrations of thermodynamic phenomena and their 
useful application. The process of making steam is one of pro- 
duction of heat by transformation from the potential form of 
energy through the action of chemical forces, and its storage 
in sensible form for later use in the steam-engine, where it is 
changed into equivalent mechanical energy. The pure science 



238 THE STEAM-BOILER. 

of the steam-engine is thus the science of thermodynamics, 
the first appHcations of which are made in the operations 
carried on in the steam-boiler. 

106. Thermodynamics is that science which treats solely 
of the relations of heat and the mechanical form of energy, of 
the establishment of the laws governing their interconversion, 
and of the applications of those laws. 

The science of thermodynamics is, as has been stated, a 
branch of the science of energetics, and is the only branch of 
that science in the domain of the physicist which has been very 
much studied. This branch of science, which is restricted to 
the consideration of the relations of heat-energy to mechanical 
energy, is based upon the great fact determined by Rumford 
and Joule, and considers the behavior of those fluids which 
are used in heat-engines as the media through which energy is 
transferred from the one form to the other. As now accepted, 
it assumes the correctness of the hypothesis of the dynamic 
theory of fluids, which supposes their expansive force to be due 
to the motion of their molecules. 

This idea is as old as Lucretius, and was distinctly ex- 
pressed by Bernouilli, Le Sage and Prevost, and Herapath. 
Joule recalled attention to this idea in 1848, as explaining the 
pressure of gases by the impact of their molecules upon the 
sides of the containing vessels. Helmholtz, ten years later, 
beautifully developed the mathematics of media composed of 
moving, frictionless particles ; and Clausius has carried on the 
work still further. 

The general conception of a gas, as held to-day, including 
the vortex-atom theory of Thomson and Rankine, supposes all 
bodies to consist of small particles called molecules, each of 
which is a chemical aggregation of its ultimate parts or atoms. 
These molecules are in a state of continual agitation, which is 
known as heat-motion. The higher the temperature, the more 
violent this agitation ; the total quantity of motion is measured 
as vis viva by the half-product of the mass into the square of 
the velocity of molecular movement, or in heat-units by the 
same product divided by Joule's equivalent. In solids, the 
range of motion is circumscribed, and change of form cannot 



HEAT AS ENERGY. 239 

take place. In fluids, the motion of the molecules has become 
sufficiently violent to enable them to break out of this range, 
and their motion is then no longer definitely restricted. The 
science of thermodynamics finds application in every phenome- 
non in which these various manifestations of heat-energy are 
accompanied by the performance of work or result from such 
work. 

107. The First Law of Thermodynamics is a simple 
corollary of the first law of energetics ; it is enunciated as fol- 
lows : 

Heat-energy and mechanical energy are mutually convertible 
and have a definite eqtiivalence. 

The British thermal unit being equivalent to 772 foot- 
pounds of work, nearly, and the metric calorie to 423.55, or, as 
usually taken, 424 kilogrammetres.* 

The first precise and direct determinations of the mechani- 
cal equivalent of the thermal unit were made by Joule, by sev- 
eral methods. He stated the results of his researches relating 
to the mechanical equivalent of heat as follows : 

(i) The heat produced by the friction of bodies, whether 
solid or liquid, is always proportional to the quantity of work 
expended. 

(2) The quantity required to increase the temperature of 
a pound of water (weighed in vacuo at 55° to 60° Fahr.) by one 
degree requires for its production the expenditure of a force 
measured by the fall of 772 pounds from a height of one foot. 
This quantity is now generally called " Joule's equivalent." 

During this series of experiments Joule also deduced the 
position of the " absolute zero," the point at which heat-motion 
ceases, and stated it to be about 480° Fahr. below the freezing- 
point of water, which is not very far from the probably true 
value, — 493°. 2 Fahr. (— 273° C), as deduced afterward from 
more precise data. 

This first law is that by the application of which we deduce 
a measure of the quantity of work done whenever a known 



foot 



* A committee of the British Association reported its value (1878)10 be 772.58 
•pounds, and a later figure is 774, with a limit of error of about two per cent. 



240 THE STEAM-BOILER. 

amount of heat is transformed ; it does not determine how much 
in any case will be transformed. For example, for any heat- 
engine we may calculate precisely how much is demanded for the 
performance of work when it is known how much work is done ; 
but this law affords no means of determining, in any such case,, 
what proportion of the heat-energy sent into the system will 
be converted into work, or what part will pass through untrans- 
formed ; and it hence gives no clue to the total quantity of 
heat called for, or of steam to be made at the boiler, even 
though all wastes by conduction and radiation be discovered 
and measured. This clue is given by the second law, which 
will also enable us to determine the amount of thermodynam- 
ically unavoidable loss. 

io8. The Second Law of Thermodynamics is stated in 
a great variety of ways by various writers, and is not always 
clearly enunciated by the best authorities. The following 
method of statement is adapted especially to present purposes : 

In the transfer or the transformation of heat-energy, the total 
effect produced is directly proportional to the total quantity of 
heat present and acting. 

Thus, if the effect of heat be to produce change of pressure,, 
change of volume, or variation of temperature, the magnitude 
of that alteration of pressure, of temperature, or of volume will 
be directly proportional to the quantity of heat concerned in 
its production. This law is based upon the almost axiomatic 
proposition, that heat-energy is homogeneous, and equal quan- 
tities must invariably be capable of causing equal effects. 

Since, in any mass of matter acting as a reservoir or vehicle 
of heat-energy, the quantity of heat present is proportional to 
its absolute temperature, it follows, from what has preceded, 
that the effect produced by any thermal variation in a heated 
mass is proportional to the absolute temperature at which the 
action takes place. These propositions and the second law of 
thermodynamics are expressed algebraically by the equations 



^dQ~' dT T dT ^> 



HEAT AS ENERGY. 24 1 

in which Q and T are the quantity of heat contained in the 
body and its absolute temperature. In other words, the prod- 
uct of the absolute temperature by the ratio of variation of 
any quantity with temperature is equal to the product of the 
heat acting into the rate of variation of that quantity with the 
variation of heat. 

The quantity of work performed by transformation of heat 
is measured by 

dW^Q^dU^T-f^dU; . . . . , (2) 

which will become know^n when the law of variation of work, 
d[/, with heat, Q, can be given. 

109. The Molecular Constitution of Matter and its physical 
structure and state determine precisely how heat will affect it, 
and just how it will behave in the storage, transfer, and transfor- 
mation of that energy into other forms. All matter consists of 
particles or molecules, sometimes simple, but usually complex, 
affected by the forces which become observable under the action 
of one body upon another. These forces are either attractive, 
repulsive, or directive. Thus, heat produces a mutual repul- 
sion of molecules, and, if permitted by surrounding masses, the 
body expands with its reception. Cohesion is an attractive 
force, as is gravitation, while magnetic and electric forces may 
be either attractive or repellent ; and the polarity seen in the 
formation of crystals and magnetism gives directive power — the 
first determining the method of aggregation of approximating 
molecules, the last the positions assumed by the molecules 
affected by it. The property of inertia is common to all forms 
of matter, and is essential to the production of all the phe- 
nomena observed in the motion and mutual actions of free 
bodies. 

no. Solids are bodies in which the attractive and directive 
forces are sufficiently powerful to give stability both of form 
and of volume. Liqiiids have stability of volume but not of 
form ; while ^^^^i" and vapors have stability neither of form nor of 
volume, and in them the repellent forces have more intensity 
16 



242 THE STEAM-BOILER. 

than the attractive. In gases the latter become insensible, and 
in the hypothetical " perfect " gas cease to exist. All interme- 
diate degrees of stability exist among the substances known in 
nature, and no known form of matter can be assigned to either 
class as a perfect representative of the combination of properties 
defining it. In passing from one state to another, substances 
traverse these intermediate conditions. Ice, water, and steam 
illustrate the three typical classes of matter. In the first the 
attractive and directive forces give stability of form and strength ; 
in the second, no stability of form exists, but some tenacity or 
cohesive power remains, which cannot be easily detected in con- 
seqience of the freedom of relative motion permitted among 
its particles when polarity disappears ; in the third form of the 
same substance the fluid must be confined within walls capable 
of sustaining its outward pressure to keep it from indefinite ex- 
pansion. 

The thermodynamic definition of a perfect gas is found in 
the equation 

pv p.v, ^ 

-Tp — -^ = /c, a constant, 

the product of pressure and volume always varying with the 
absolute temperature. 

III. Heat and Matter have this peculiar relation, that 
while all other forces which commonly, with that due to the 
presence of heat, determine to which of the three physical states 
the latter shall be assigned, are definitely related to the sub- 
stance, having magnitudes Avhich are functions of volume and 
of molecular distances, the force introduced with heat, and 
which is always repellent, is variable, independently of all other 
conditions, and is, in fact, constantly so varying. 

It is the introduction or the removal of heat energy from mat- 
ter which produces all familiar physical changes of states. When 
a solid is heated it is expanded against the resisting efforts of all 
other internal and external forces, and after a time the quan- 
tity of heat and the temperature attaining a limit which is per- 
fectly definite for each substance, the directive force becomes 



HEAT AS ENERGY. 243 

insensible, and the mass becomes liquid. The introduction of 
heat continuing, the separation of molecules continues until the 
cohesive force becomes insensible, or at least less than the ex- 
pansive force of the heat, and the fluid is converted into a 
vapor ; and finally, when the attractive forces disappear en- 
tirely, into gas. In this process, internal forces being overcome, 
internal work is performed, and external forces being overcome, 
external work is done ; while a certain amount of heat, not so 
expended, is added to the mass as sensible heat, and thus raises 
its temperature. 

Specific Heats measure the quantity of heat absorbed by unit 
weight of any substance in a change of temperature of one 
degree, the heat being either all or partly unchanged. It has 
been already defined and values given in § 91. Thermodynam- 
ically considered, it is seen specific heats may measure either 
heat or w^ork, or both. 

112. Sensible and Latent Heats must be carefully distin^ 
guished in studying the action of heat on matter. The term 
" sensible heat " scarcely requires definition ; but it may be said 
that sensible and latent heats represent latent and sensible 
work ; that the former is actual, kinetic, heat-energy, capable of 
transformation into mechanical energy, or vis viva of masses, 
and into mechanical work; while the latter form is not heat, 
but is the equivalent of heat transformed to produce a visible 
effect in the performance of molecular, or internal as well as 
external, work, and visible alteration of volume and other phys- 
ical conditions. 

It is seen that heat may become ''latent" through any 
transformation which results in a definite and. defined physical 
change, produced by expansion of any substance in consequence 
of such transmutation into internal and external work ; whether 
it be simple increase of volume or such increase with change 
of physical state. 

113. The Latent Heat of Expansion is a name for that 
heat which is demanded to produce an increase of volume, as 
distinguished from that untransformed heat which is absorbed 
by the substance to produce elevation of temperature. The 
latent heat of expansion may, by its absorption and transforma- 



244 THE STEAM-BOILER. 

tion, and the resulting performance of internal and external 
work, cause no other effect than change of volume, as, e.g.^ 
when air is heated ; or it may at the same time produce an 
alteration of the solid to the fluid, or of the liquid to the 
vaporous state, as in the melting of ice or the boiling of water, 
in which latter cases, as it happens, no elevation of temperature 
occurs, all heat received being at once transformed. In the 
expansion of air, and in other cases in which no such change 
of state occurs, a part of the heat absorbed remains unchanged, 
producing elevation of temperature ; while another part is 
transformed into latent heat of expansion. 

The specific heat of constant volume, no molecular or other 
work being done, measures the heat untransformed, and, as 
sensible heat, producing rise in temperature. The specific heat 
of constant pressure measures the sum of the sensible and latent 
heats, when a gas is heated, and no alteration of physical state 
can occur. It usually is assumed to include both internal and 
external work, as well as sensible heat, but where used in an 
unaccustomed sense the conditions of the case are always 
stated. 

114. The Latent Heats of Fusion and of Vaporization 
measure the quantities of heat transformed in these changes of 
physical state. In the first of these two cases the work done 
is mainly internal ; in the second the internal work performed 
is much greater, but is not so enormously in excess of the 
amount of external work done; and the higher the pressure 
under which vaporization takes place, the larger proportionally 
the measure of external work and of the heat demanded for its 
performance. In the case of steam, as will be seen later, at 
ordinary pressures, the ratio of internal to external work in 
this change of state is about as ten to one. All this work is 
performed in the expansion of the mass against resisting molec- 
ular attractive forces, unperceivable and incapable of measure- 
ment by any ordinary pressure-gauge or physical instrument. 

115. The Distribution of Heat Energy in thermodynamic 
operations, and in physical changes produced by it, must be 
carefully studied, and must be represented in every algebraic 
expression in the mathematical theory of the subject. As has 



HEAT AS ENERGY. 245 

been fully shown, the absorption of heat by any substance often 
involves, and may in any given case involve, three different 
applications ; it may be appropriated to the elevation of tem- 
perature; to the expansion of the mass against internal forces, 
doing internal work ; or to the increase of its volume, overcom- 
ing external pressures and performing external work. On the 
other hand, if heat is received from any substance, it may be 
sensible heat simply transferred without change ; or it may be 
heat produced by transformation out of work through the action 
■of cohesive forces ; or it may be heat similarly resulting from 
the work done by external pressure on the mass during its com- 
pression. 

Whatever the manner in which heat-energy is transferred 
or transformed, such phenomena as are observed during the pro- 
cess are subject to the principles which have been stated, and the 
theory of the process is constructed by the application of the 
two laws which have been enunciated, and in that manner only. 
Every algebraic expression representing such a process will be 
a statement of equality between the total amount of heat- 
energy entering or leaving the substance, and the sum of the 
variations of sensible and latent heats in the mass affected. 

116. The Application of the First Law leads at once to 
the construction of the fundamental equations of thermody- 
namics, and permits the determination of their constants. The 
first equation to be established is simply a statement, in alge- 
braic language, of the fact that the total quantity of heat ab- 
sorbed or rejected by any substance during any elementary 
change must be the sum of the variation of the sensible heat 
of the mass and of the latent heats. The convertibility of the 
thermalunit into the mechanical unit of w^ork or energy renders 
it a matter of indifference which unit is adopted. If Q repre- 
sent heat measured in thermal and H the same quantity in 
mechanical units, and ify be taken as the symbol of the me- 
chanical equivalent of heat, and A ^=^ -j. the thermal equivalent 

of the mechanical unit, we may write at once, as the expression 
of the first law of thermodynamics, 

dH ^ JdQ = KdT + dW, (i) 



246 THE STEAM-BOILER. 

in which equation K is the dynamical specific heat, or in sym- 
bols CJ, the product of the thermally measured specific heat, 
C, by Joule's equivalent ; T the absolute temperature ; 5 the 
sensible and PFthe total latent heat, measured in mechanical 
units. 

Hereafter all measurements will be given in mechanical 
units, unless otherwise stated. 

Separating the heat doing the work, W^ as distinguished 
from other heat, into two parts, the one, Z, the internal latent 
heat, the other, U^ the latent heat of external work, 

dH = JdQ = dS + dL + dU, .... (2) 

and making the '' internal energy," as it is sometimes called, 
Ey the sum of the sensible heat and internal work, 

dH=dE + dU. (3); 

Or, otherwise exhibited, 

dH = 



dS + ~dW 



dL + dU 



dE + 

And these expressions are true for all substances and for all 
possible cases. 

The sensible heat being the product of the specific heat into 
the range of temperature, and work being always the product 
of the alteration of volume into the intensities of the mean re- 
sistance, the preceding equations may be written : 



dH=KdT+{p,+J>,)dv . ,. 

= KdT+pdv; ' ^^' 



HEAT AS ENERGY. 247 

when//,/^, and / represent respectively the internal, the ex- 
ternal, and the sum of internal and external forces, and v is the 
volume of the mass, which is assumed to have unity of weight. 
. When, as here, the two independent variables are tempera- 
ture and volume, 

dH^f^T+'-gdv, (5) 

and, from the preceding, we thus find 

dH ,^ dH 

-dT-^'^ ^=^' (^) 

and the values correspond with the definitions already given. 

117. The Application of the Second Law of Thermo- 
dynamics establishes some important modifications of the 
equations just derived. Since every effect is proportional to 
the quantity of heat acting to produce it, and hence to the ab- 
solute temperature of the mass, 

dH=TdQ = dS^dW; (i) 

in which expression is that'' thermodynamic function" which, 
being multiplied by the absolute temperature, will give a prod- 
uct measuring the quantity of heat demanded or rejected in the 
production of the change. Again, since dW =: pdv, and since, 
according to the second law, the total pressure,/, must be equal 
to the product of the absolute temperature at which the change 
occurs by the rate of variation of pressure with temperature, 
dp 
If' 

dH=TdQ = KdT-^T^dT', . . . . (2) 

and the form and value of the thermodynamic function be- 
comes at once determinable : 



248 THE STEAM-BOILER. 

^dH _ n dp 



Q=f^~ = K^\og.T-^f-^dv (3) 



By a process which need not be here described, and which 
can be seen in every treatise on thermodynamics, an equation 
of somewhat similar form, but in which the variables taken are 
Zand/, is obtained, thus: 

dH=TdQ = Kj,dT-T-^dp', , ... (4) 

i /* dTJ 

Q^K,\og,T-J ^dp. (5) 



The fundamental equations of thermodynamics are thus 
completely established. As here given they are general, and 
applicable to all substances. In the present work, however, 
Ave are only concerned with their application to the operation 
of thermodynamic changes occurring in water and steam. 

ii8. The Computation of Internal Forces and Work, 
and of external work, are now easily effected. Notwithstand- 
ing the fact, as already stated, that the molecular forces, and 
the work performed by or against them, are beyond the reach 
of any physical apparatus and are incapable of direct measure- 
ment, it becomes easy to calculate both force and work from 
measurable data by application of the second law of thermo- 
dynamics. 

The rate of variation of external pressure and work with 
temperature, at constant volume, may be determined easily by 
experiment ; this rate, according to the second law, is constant 
for all temperatures, and hence, being multiplied by the abso- 
lute temperature at which the total pressure or the work is to 
be determined, the product measures that total pressure or 
work. In symbols, let/, w, and 7^ represent the total pressure 
and work, and the absolute temperature ; then the rates of va- 

. . dp dzv . , , . I , r 

nation -3^, -jj., with temperature may be ascertained by, for 



HEAT AS ENERGY. 249 

example, noting the change of external pressure, as measured 
by the steam-gauge, for a change of one degree or other small 
but exactly measurable range, and taking this ratio of differences, 

--7^, as sensibly equal to -3^, The work-ratio is obtained by 

multiplying the Ap by the volume and taking this product. 

Aw dw 
Ap'V = Aw, as the numerator in -jj-— -yj-- Then the total 

pressure, internal and external, must be measured by 

/=#. ....... (0 

and the total work of expansion from zero 

dw dp 
""= ^dT = ^dT'' (") 

It thus becomes possible readily to determine the inter- 
nal and external pressures, the internal and external work, and 
the latent heats of the vapors, or of any other imperfectly 
gaseous or non-gaseous substance. 

Since the heat rendered latent, in any case, is the equivalent 
of the work performed by it, the latent heat of vaporization 
must be exactly equal, dynamically, to the work just measured, 
and if it be called H for unity of weight, 

^=^%=^P- • • • • • (3) 

when Av is the increase of volume taking place during the 
change of physical state. If the value is made known, as is 
usual, by experiment, and Av is observed, it becomes easy to 
obtain 

dp _ T{v,- V,) 

dT- H • ...... (4) 

dp 
The value of -3^ is sometimes found to be negative, e.g., in 



250 THE STEAM-BOILER. 

the case of ice. Professor James Thomson found 

dp 
— ^= o°.oi33 Fahr. = o°.oo74 Cent. 

as the amount by which the melting-point of ice is lowered by 
every increase of one atmosphere of pressure. The latent heat 
of fusion is similarly measured. The total heat of vaporiza- 
tion, as it is called, from a temperature T^ and at a tempera- 
ture 7*2, is the sum of the latent heat converted into work, as 
just measured, and the sensible heat demanded to raise the 
temperature from Z", to T^. 

The latent heat of vaporization per unit of volume is ob- 
viously measured by 

L = = T-J^', (5) 

v^ — v^ dT ^•'^ 

and this permits the ready calculation of the heat demanded in 
supplying any steam, or other vapor, engine with the quantity 
of fluid required to do any given amount of work, or to drive 
its piston through any given space, and this without knowing 
the density of the fluid. The rate of variation of the pressure 
of the vapor at the boiling-point, with temperature, may be 
obtained from the tables, or from formulas such as have been 
given for steam by Regnault, and for that and other vapors by 
Rankine."^ The latter are the most general and usually the 
most exact ; they have the form 



whence 



B C 

log/ = ^ — y — y^ ; (6) 



dp IB 2C\ 

~dT "" ^\T + Ty ^^' ^°' * • • ^^^ 



The density of vapor may thus be readily computed from 
the known value of its latent heat, and much more satisfactorily 

* Steam-engine, § 206, Div. III. 



HEA T AS ENERGY. 25 I 

and exactly than it can be derived by any known method of 
experimental determination. The increase of volume of unity 
of weight must always be 

'v.-'v.^^\ (8) 

in which, practically, the values of v^ may usually be neglected. 
Then the density"^ is 

D='-^~_ ....... (9) 



* Tables thus calculated for steam and for ether and other fluids are given by 
Rankine in his Miscellaneous Papers and in his treatise on the Steam-engine. 



CHAPTER VI. 

STEAM AND ITS PROPERTIES. 

119. The Production and Use of Steam involves so im- 
portant and interesting a series of physical phenomena that 
they are deserving of special study. The generation of steam, 
and its supply to the steam-engine or other apparatus in which 
it finds application, is a process: first, of heating the "feed- 
water" from the temperature at which it is supplied up to that 
at which it is vaporized ; secondly, the change of its physical 
state at the latter temperature; thirdly, its expansion into a 
vapor; and finally, in some cases, the drying and even the 
superheating of the steam so formed until it assumes the truly 
gaseous state. 

The water supplied to the steam-boiler often comes from 
rivers or smaller streams, sometimes from springs, occasionally 
from rain-water cisterns, and, at sea, either from condensers or 
stills, or from the ocean. Each one of these sources of supply 
provides water having properties characteristic of its origin, and 
fitting it, or unfitting it, as the case may be, more or less per- 
fectly for its use in the boiler. The study of the properties of 
pure water, of its composition and chemical and physical char- 
acter, and of the nature and effects of the impurities dissolved 
or mechanically suspended in it, is thus made essential to an 
intelligent understanding of the problems presented to the 
engineer who designs, builds, or operates the steam-boiler. 
The chemistry and physics of water and steam, and of their 
changes of state and properties, must be studied in connection 
with the thermodynamics of steam in its application as a vehicle 
and a reservoir of heat-energy; and with this study must be 
combined also, and especially, that of the relations of heat and 
steam to mechanical power as developed by transformation of 
heat in the steam-engine. This latter division of the subject is 
commonly reserved for treatises on the steam-engine. 



STEAM AND ITS PROPERTIES. 253 

120. The Properties of Water, as noted by the senses, are 
familiar to all. It occurs universally distributed throughout the 
world, in earth, air, and sea, in its three forms, ice, water, and 
vapor, and in its most common and familiar form covers three 
fourths of the surface of the globe. As ice and snow it per- 
manently covers the arctic regions and the tops of lofty moun- 
tains, and as vapor it forms an important constituent of the 
atmosphere. When pure, it is absolutely free from either taste 
or smell, and is colorless, except that in very large masses it 
assumes a beautiful blue tint. In the form of ice it weighs 
about 55 pounds per cubic foot (0.9 kilog. to the litre, nearly), 
and has considerable tenacity, while yet capable of flow, with 
breaking up and " regelation" under pressure. 

In the liquid state it still retains considerable cohesive 
force, but the lack of polarity among its molecules, and its con- 
sequent instability of form, so modify its properties that this 
tenacity cannot be perceived except by the adoption of special 
expedients directed to that end. Converted into vapor or 
steam, it assumes all the characteristics of the gases, except that, 
like other vapors, at temperatures and pressures near the boil- 
ing-point it gives evidence of the imperfection of its gaseous 
state by more rapid variation of pressure with temperature than 
the laws of the gases would indicate. Heated above the tem- 
perature of its boiling-point it rapidly takes on the properties 
of a true gas, and conforms to the laws of Boyle and Marriotte, 

PV 
and of Charles and Gay-Lussac, and the expression -— = 

constant then becomes sensibly correct. 

Water is the most efificient of all known solvents, and under 
certain conditions dissolves nearly all kinds of matter, even at- 
tacking glass and other mineral substances at high temperatures 
and pressures. Its action on metals is often marked, and is 
sometimes ver}^ serious. It dissolves lead rather freely, so 
much so that lead-poisoning not infrequently occurs from the 
presence of that metal in drinking-water held in contact with 
it. The presence of carbonic acid in observable amount, how- 
ever, seems essential to the rapid solution of lead, as it invaria- 
bly is in oxidation. The lead in solder is dissolved more freely 



254 



THE STEAM-BOILER. 



than pure lead alone. Water, especially when containing car- 
bonic acid, dissolves iron and copper rather freely ; its presence, 
either as liquid or as vapor, is absolutely essential to the cor- 
rosion of iron ; both moisture and carbon dioxide are invariably 
present when iron " rusts" rapidly. 

Bunsen gives the following as the coefficient of absorption 
by water at the given temperatures, for familiar substances i"^ 



Temperatures. 



Hydrogen 

Oxygen 

Nitrogen 

Atmospheric air 

Carbon dioxide 

•' monoxide . . . 

Carb. hydrogen, CH4. 

C2H4 

Sulph. " 

Ammonia 



Cent. 0°. 
Fahr. 32*^ 



.01930 
04114 
.02035 
.02471 
,7967 
03287 

05449 
0.2563 
4.3706 
1049.6 



0.01930 
0.03250 
0.01607 
0.01953 
I. 1847 
O.Q2635 
0.04372 
0.1837 
3.5858 
I12.8 



68= 



0.01930 
0.02838 
o . 00403 

0.01704 

0.9014 

0.02312 

0.03499 

0.1488 

2.9053 
654.0 



121. The Composition of Water and its chemistry are 
Avell understood in all its technical relations. Cavendish showed 
its constitution by synthesis in 1781 ; Humboldt and Gay-Lus- 
sac, in 1805, found it to consist of one volume hydrogen and 
two volumes oxygen ; while Berzelius and Dulong determined 
its proportions by weight, hydrogen one and oxygen eight, i.e., 



Ha 
O 

H2O 



Molecular 
Weight. 

2 

16 

18 



Calculated. 
II. Ill 
88.888 

100 . 000 



Berzelius 
and Dulong. 

II. I 

88.9 



Dumas. 
II, II 



100. o 



Lavoisier made the composition of water one of the bases of 
his new system. 

Water is a neutral compound, exhibiting, when pure, neither 
acid nor alkaline reaction ; but so freely does it dissolve sub- 
stances with which it is brought in contact, that it is rarely 
found in nature absolutely free from either acidity or alkalinity. 
Its presence is essential to nearly all the chemical operations of 
nature, as well as in the laboratory. 



* Methods of Gasometry. 



STEAM AND ITS PROPERTIES. 255 

The fluid may be decomposed in either of several ways, as 
by heat alone, a process of '' dissociation" of its elements tak- 
ing place at between 2000° and 4000° Fahr. (1100° to 2200°C.), 
or by the voltaic current, and by the action of various metals or 
metalloids at high temperatures, when the substance employed 
has a strong affinity for the oxygen, as have carbon, iron, etc. 

Water is found wherever hydrogen is burned, in air or oxy- 
gen, either alone or in combination with other elements. It 
enters into combination with many other substances, and as 
water of crystallization, for example, often influences the char- 
acter of the compound to a very important degree. 

122. The Sources and Purity of Water demand careful at- 
tention from the engineer proposing to use it in the production 
of steam ; since the presence of any foreign matter is always 
productive of some and sometimes of serious difficulties, and 
even of dangers. Rain-water is the purest of all natural waters ; 
but even rain-water contains all such gaseous substances in 
solution as may have been dissolved in its fall through the at- 
mosphere, and such minute quantities of organic and other 
solid matter as are found floating in the air. The volume of 
dissolved gas is usually about 25 parts in 1000 of water. As 
oxygen dissolves more freely than nitrogen, their proportions 
in solution differ from those of the atmosphere, averaging not 
far from one third oxygen and two thirds nitrogen. 

Spring-waters hold in solution every soluble element or com- 
pound found in the rocks and soils through which they flow. 
The purest of them are those '' soft" waters rising from gra- 
nitic formations ; those of limestone districts contain, often, con- 
siderable quantities of lime, and are very " hard." Spring-waters 
are often so heavily charged with dissolved substances as to be 
useless for domestic or manufacturing purposes. Good spring- 
water is, however, often found "fresh" and pure, and such water 
should always be sought for use as " feed-water" for steam-boil- 
ers. 

River- water is usually purer than spring-waters, even although 
largely consisting of such waters. The dilution of the stream by 
surface-water, the precipitation of lime and other salts held in 
solution only by carbonic acid, which is set free on exposure to 



256 l^HE STEAM-BOILER. 

the atmosphere, and the purifying influences of the atmosphere,, 
all together may very greatly reduce the proportion of impurity. 
River-water is apt to contain more organic matter than does 
spring-water; this is sometimes, though rarely, dangerous in 
boilers. It is liable to contain large quantities of sand, clay, or 
other kind of soil, mechanically suspended ; but this can usually 
be removed sufficiently well by filtering. 

A water carrying a considerable amount of the carbonate of 
lime and other alkalies in solution, and used in the boilers of 
locomotives in the Mississippi valley, deposited a scale having 
the following analysis : 

Iron peroxide 5 . 700 per cent. 

Silica 2.960 " 

Potassa 5-131 

Alumina 320 '* 

Soda 2.137 ** 

Sulphuric acid 006 ** 

Lime ... 24.760 ** 

Magnesia 8.294 " 

Carbonic acid. 41 . 060 ** 

The effect was to produce some leakage and marked loss of 
economy. This may be taken as a fair sample of the incrusta- 
tion to be expected in limestone districts. 

123. Sea-water is a " mineral water," strongly saline, con- 
siderably chlorinated, and slightly alkaline. The composition 
of the water of the ocean differs very slightly in different local- 
ities. It contains about ^^ of its own weight of salts, mainly 
common salt, with various other chlorides and bromides, and 
some gases. 

The following analysis was made by Von Bibra : 

Sodium chloride 1671.34 

Magnesium chloride 199.66 

Sodium bromide ' 31 . 16 

Potass, sulphate 108 . 46 

Magnes. " 34-99 

Calcium " 93-30 

Total in i U. S. gallon 2138.91 grs., 

or 3.569 per cent, by weight. 



STEAM AND ITS PROPERTIES. 2$^ 

Forschammer finds for each lOO parts chlorine: 

SO4 Mg Ca Total. 

Maximum '. 14.51 6.768 2.257 181.40 

Mean 14.26 6.642 2. 114 181. 10 

Minimum 13-98 6.570 2.050 180.60 

In some inland seas, as the Great Salt Lake and the Dead 
Sea, the proportion of saline matter is enormously greater. 
Herapath found the latter to contain 19.73 per cent solid mat- 
ter, of which one half was common salt, and one third magne- 
sium chloride ; the next largest constituents were the calcium 
and potassium chlorides and sodium bromide. 

Deposits from sea-water, and from any other water contain- 
ing solid matter either in solution or suspended, will always 
occur on evaporating the water ; and these deposits form the in- 
crustation and sediment which endanger the steam-boiler and 
reduce the efficiency of its heating-surfaces. They are pre- 
vented at sea, usually, by the adoption of the surface-condenser, 
or by the process of " pumping and blowing" where the jet-con- 
densen is employed, and when the sea-water is thus unavoid- 
ably used in the boiler. This will be referred to in describing 
the operation and management of the marine steam-boiler. 

The salts in sea-water are not precipitated at the boiling- 
point ; but, in a concentrated solution at 217° Fahr. (102'' 
Cent.), sulphate of lime begins to come down, and at the tem- 
peratures customarily met with in marine steam-boilers it is all 
deposited. A saturated solution of common salt is obtained at 
a temperature of about 230° Fahr. (i 10° Cent.) and at one tenth 
the volume of the sea-water, the salt having increased in its per- 
centage from 3 to 30. A cubic foot of sea-water weighs about 
64 pounds, or |^ that of fresh water, the one measuring 35 and 
the other 36 cubic feet to the ton, nearly. The boiling-point of 
salt water rises about i"°.2 Fahr. (o°.7 Cent.) for every 3 per 
cent of salt added up to the point of saturation. (See § 126.) 

The character of the water in a marine steam-boiler, after 
long working, and with the usual moderate concentration, is 
shown by analyses made for the Author by Dr. Albert R. 
Leeds, the report on which was as follows : 
17 



258 the steam-boiler. 

Examination of Waters from a Marine Boiler, with 

REFERENCE TO CAUSES OF RAPID CORROSION OF HEATING- 
SURFACES. 

Samples. 

I. Forward end of boiler ; 2, after end of boiler ; 3, hot well. 

Preliminary Instr2Lctions and A nalyses. 

The instructions were to examine for organic acids and 
copper. 

All the organic acids that could possibly occur under the 
circumstances were looked for in Nos. i, 2, and 3. None pres- 
ent. 

Of copper, none was found except in No. i, and then only 
a trace when the examination was repeated on a larger quan- 
tity of liquid. If the quantity of water at my disposal had 
not been so limited, a similar examination of No. 2 might have 
revealed a trace of copper in it also. 

These results being inadequate to explain the causes of cor- 
rosion, the following analyses were required : 

ANALYSES OF THREE SAMPLES. 

Amount of Solid Matter in Waters. 

1. 100 cubic cent 4 . 562 grammes. 

(Corresponding to about 6.1 oz. in i U. S. gallon.) 

2. 100 cubic cent, contained 4.8386 " 

3. 100 " " " 0.2680 ** 

Loss by Ignition. 

These residues were obtained by drying at 110° C. On ig- 
nition, water was given off, and a partial decomposition, attended 
with loss of chlorine, ensued. But unlike many samples of 
water, the loss by ignition in these cases is not to be attributed 
to organic matter present. 

No. I lost 9 . 43 per cent. 

" 2 " ... 6.01 

" 3 " ...-. 1511 



STEAM AND ITS PROPERTIES. 259 

Results of Qualitative Analysis. 

I. 2. 3. 

Organic acids None. None. None. 

Chlorine Present. Present. Present. 

Ammonia None. None. None. 

Lime None. Trace. None. 

Magnesia Abundant. Abundant. Abundant. 

Oxide of iron None. None. None. 

Copper Trace. None. None. 

Sulphuric acid Present. Present. Present. 

Sodium Large. Large. Large. 

Bromine, Uot tested for. 
Iodine, ) 

The most striking feature is the large amounts of the chlo- 
rides and sulphates of the alkalies and magnesium — more espe- 
cially the magnesium salts. 



Specific Gravities and other Properties. 

Specific gravity of No. i 1.0300 15° C. 

" ** *' 2 1.0309 •' 

** ** " 3 1.0030 *' 

I was slightly turbid from suspended matter, but colorless ; 
2, turbid, and of a slightly pinkish color; 3, colorless and clear. 

It will be noticed that the specific gravities of Nos. i and 2 
are somewhat greater than the average specific gravity of sea- 
water, which is 1.027. 



Corrosive Properties of the Water. 

Ex. I. — A galvanic pair was made of a plate of copper and 
one of iron, separated below but in contact above the liquid. 
On immersion into water No. i hydrated sesquioxide of iron 
was rapidly formed. No notable deposit of copper could be 
detected on the iron plate, and no trace of copper in the liquid. 
If the minute trace of copper was precipitated out, the coating 
was too slight to be visible. 

Ex. 2. — A sheet of iron alone was immersed in the water No. 
I at the boiling-point. Oxide of iron was formed, but in much 
less quantity than in Ex. i. 



26o THE STEAM-BOILER. 

Ex. 3. — A galvanic pair, as in Ex. i, was put in the circuit 
of a galvanometer. On making contact a large deflection took 
place, showing high tension, the needle coming to rest with a 
permanent deflection of 3°. At the same time oxidation of the 
iron went on rapidly. 

Conclusions, 

That water having a composition as above given, and with- 
out organic acids, is capable of producing corrosion of the iron ; 
that such water, when it is the exciting fluid in a galvanic com- 
bination, one element of which is iron, the other copper, pro- 
duces a galvanic current of notable quantity and intensity. 
Under such circumstances corrosion of the iron takes place 
more rapidly than when iron alone is in contact with the liquid. 

124. Technical Uses and manufacturing operations com- 
monly require the purest possible water. In the steam-boiler, 
especially, where all the water evaporated necessarily leaves 
behind every particle of solid matter held in solution at its in- 
troduction, purity of the fluid is of great importance. Half a 
ton of lime " scale" has been taken from the boiler of a locomo- 
tive, and the Author has seen several tons of salt and scale in a 
large marine boiler which had been ruined by its presence, and 
the consequent destruction of its furnace and furnace-flues by 
overheating and oxidation. Boiler explosions have often been 
caused by such incrustations. The prevention and removal of 
scale is a matter of serious importance in steam-boiler manage- 
ment, and will be considered later. It may be stated here that 
various chemical reagents are relied upon to produce a remov- 
able and comparatively safe form of salt-deposit, and heating 
and filtration of the water before it enters the boiler are usually 
the best preventives. 

Filtration by means of filter-beds for large volumes of 
water, and by filtering apparatus of various kinds, may always 
be relied upon to remove the undissolved solid matter. Filtra- 
tion is often combined with heating and sometimes with chem- 
ical treatment in the purification of water. 

The temperatures at which calcareous matters are precipi- 
tated in ordinary boiler waters are as follows : 



I 



STEAM AND ITS PROPERTIES. 26 1 

Carbonates of lime, between 176° and 248" Fahr. (80° to 120° C.) 

Sulphates of lime, between 284° and 424° Fahr. (140° to 218° C.) 

Chlorides of magnesium, between 212° and 257° Fahr. (100° to 124° C.) 

Chlorides of sodium, between 324° and 364° Fahr. (160° to 184° C.) 

In order to free water from these salts it must consequently 
be heated to the above temperatures. 

125. Water-analysis is often resorted to by the engineer 
to determine the proportion of scale-forming constituents in 
water to be used in steam-boilers. The determination of the 
specific gravity is sometimes a first step ; but the variations 
from that of pure water are usually too slight to be observable. 
Where it is taken it is best done by weighing on the chemist's 
balance. Color is observed by filling a long glass tube, cap- 
ping the ends with plate glass, and looking through it at a 
white background, beside a tube similarly prepared containing 
pure water. The smell and taste are noted, both cold and 
warm, and the water is tested with litmus-paper to detect any 
acidity or alkalinity ; should the paper turn blue, and again 
lose the color on exposure to the air, ammonia is indicated. 

The total dissolved solid matter contained is ascertained by 
evaporating to dryness, after filtration, and weighing the de- 
posit. The final drying is usually completed in a steam-bath 
at the boiling-point, 212° F. (100° C). The weight of fixed 
mineral contents is then estimated by igniting until all organic 
matter is decomposed and its carbon burned away, and the loss 
of weight noted. The suspended matter may be weighed from 
the filters, or may be obtained by allowing it to settle in a still 
tank or large bottle until the water is perfectly clear, decanting 
and weighing after drying. 

The ^^ hardness' of water is gauged by several methods, of 
which Clark's is one of the best. It depends upon the fact that 
when water is pure it froths when shaken up with an alcoholic 
solution of soap ; while if mineral salts are present it remains 
free from " suds" until a considerably increased amount of soap 
is introduced. The quantity of soap required to produce ob- 
servable frothing is a fairly good gauge of the hardness of the 
water. This hardness is measured in "degrees," each of which 
is equal to o.oi gramme of calcic carbonate, or its equivalent, 



262 . THE STEAM-BOILER. 

to the litre, i.e., one part in 100,000. The standard solution is 
made by dissolving white curd-soap in alcohol of 0.92 s. g., 
until 100 cubic centimetres will make a froth with an equal 
quantity of water of 20° hardness. This is preserved in glass- 
stoppered bottles, and sometimes diluted to make other stan- 
dard solutions. The presence of a considerable proportion of 
magnesian salts causes the indication of this test to be de- 
fective, giving too low a figure for the hardness. 

Carbonates precipitated by boiling are dried and weighed. 
Organic matter is calcined and so determined roughly, or may 
be measured by reaction with potassic permanganate. The 
amounts of the several solid constituents are customarily ex- 
pressed as parts in 1,000,000, by weight, of the water ; some- 
times as grammes in the litre, and also as grains to the gallon : 
the last may be reduced from the next preceding by multiply- 
ing grammes per litre by 0.07; they can be converted into 
degrees on Clark's scale by multiplying by 0.7. Cubic centi- 
metres per litre may be converted into grains per gallon by 
dividing by 3.738. 

126. The Purification of Water is often essential both 
for sanitary and commercial purposes. The first and simplest 
process of purification of water containing dissolved substances 
is distillation. The liquid is boiled in closed vessels, and the 
steam conducted into a condenser, and there restored to the 
liquid state by cooling. All salts and solid matters are left be- 
hind in the evaporating vessel, and the distilled fluid is abso- 
lutely pure if the process is conducted in vessels of insoluble 
metal or of glass. In many cases the lime salts are precipitated 
by simple heating without vaporization, the solid precipitate 
coating the surfaces of the heater or the stone or other masses 
with which it is sometimes partly filled. The addition of com- 
mon washing soda is better than the use of the nostrums sold 
as "scale preventives." The safest course is always to have 
the water analyzed, and thus to ascertain the best method of 
treatment. Saccharine and amylaceous matters and extractive 
substances are useful in preventing the deposition of lime and 
magnesian carbonates in a hard scale, and barium chloride is 
effective in a similar manner, where the water contains calcic 



STEAM AND ITS PROPERTIES. 263 

sulphate. Water may be purified of its lime salts, the lime 
being held in solution as a bicarbonate, by the addition of lime- 
water, which takes a part of the carbonic acid and causes com- 
plete precipitation. This process has been used in the purifi- 
cation of feed-water for use in steam-boilers ; but the great 
quantity of water used generally makes it a somewhat expen- 
sive system. M. E. Asselin recommends the use of glycerine 
to prevent incrustation in steam-boilers. 

Glycerine soluble in water in every proportion increases the 
solubility of combinations of lime, and especially of the sul- 
phate ; it appears besides to form with these combinations 
soluble compounds. When the quantity of lime becomes so 
great that it can no longer be dissolved, nor form with the 
glycerine soluble combinations, it is deposited in a gelatinous 
substance, which nev^er adheres to the surface of the iron 
plates. Moreover, the gelatinous substances thus formed are 
not carried with the steam into the cylinder of the engine. 

M. Asselin advises the employment of one pound of gly- 
cerine for every 300 or 400 pounds of coal burnt, fifteen days' 
supply being introduced at once. Glycerine combines with all 
the salts, and leaves the plates perfectly clean. 

Filtration, as has been already stated, is the process by which 
all mechanically-suspended matter is removed from water (§ 124). 

127. The Physical Characteristics of Water, when pure, 
are the following: Its density is about 770 times that of air, and 
is a maximum at about 39^.2 Fahr. (4° Cent.), with exceedingly 
slight variation through ordinary ranges of temperature. This 
is taken as unity, and as a standard for all densimetric determi- 
nations with solids or liquids. Water is perfectly elastic with 
a very great modulus ; at low temperatures the compressibility 
increasing with temperature, and decreasing with its solution 
of salts. Grassi, Amaury and Descamps, and Cailletet, all 
find the coefficient of compressibility at mean atmospheric 
temperature to be 0.000045 to 0.000046. At the freezing- 
point it becomes 0.00005. 

On the application of heat, water expands from unity to 
1.043, i^ passing from the freezing to the boiling point. It has 
a very high heat-capacity, which is taken as unity in comparing 



264 



THE STEAM-BOILER. 



specific heats of other substances. It is an almost perfect non^ 
conductor of heat, and only transfers heat readily by convec- 
tion. Its conductivity in absolute measure is about o.(X)2. On 
reducing its temperature to 32° F. {0° C.) water freezes, and 
the ice produced has a specific gravity, when solid and pure, of 
0.92, and floats on the surface of water at the same tempera- 
ture. The expansion observed at freezing takes place with 
immense force, and often bursts water-pipes when they are 
frozen up. The boiling-point of water, under atmospheric pres- 
sure, is at 212° Fahr. (100° Cent.), and very variable, as shown 
later, with change of pressure. The boiling-point also rises with 
the increase of density by the solution of other substances. 

One cubic foot of water weighs 62.425 pounds at maximum 
density, or nearly 1000 ounces (62.5 pounds). The cubic metre 
weighs 1000 kilogrammes. One atmosphere counterbalances a 
column of water 33.95 feet (10.35 i^-) high. 

The following table gives the volume and weight of dis- 
tilled water at various temperatures : 



t 

3 

a! 

a 

I 


Ratio of 
volume to 

that of 

equal 

weight at 

maximum 

density. 


Weight 
of a 
cubic 
foot. 


3 
6 


Ratio of 

volume to 

that of 

equal 

weight at 

maximum 

density. 


Weight 
of a 
cubic 
foot. 


3 

B 


Ratio of 

volume to 

that of 

equal 

weight at 

maximum 

density. 


Weight 
of a 
cubic 
foot. 


Faki 


r. 


Lbs. 


Fah 


^. 


Lbs. 


Fah 


K. 


Lbs. 


32 


° I. 000129 


62.417 


210 


° 1.04226 


59 


894 


390 


1-15538 


54 030 


39 


I I . 000000 


62.425 


212 




04312 


59 


707 


400 


I. 16366 


53-635 


40 


I . 000004 


62.423 


220 




04668 


59 


641 


410 


I.I7218 


53-255 


50 


1.000253 


62.409 


230 




05142 


59 


372 


420 


1.18090 


52 862 


60 


1.000929 


62.367 


240 




05633 


59 


096 


430 


I. 18982 


52.466 


70 


I.OOI981 


62.302 


250 




06144 


58 


812 


440 


I. T 9898 


52.065 


80 


I .00332 


62.218 


260 




06679 


58 


517 


450 


1.20833 


51.662 


90 


I .00492 


62.119 


270 




07233 


58 


214 


460 


1.21790 


51.256 


100 


1.0C686 


62.000 


280 




07809 


57 


903 


470 


1.22767 


50.848 


no 


I . 00902 


61.867 


290 




08405 


57 


585 


480 


1.23766 


50.438 


120 


1.01143 


61.720 


300 




0Q023 


i'7 


259 


490 


1.24785 


50.026 


130 


1.01411 


'61.556 


310 




09661 


56 


925 


500 


1.25828 


49.611 


140 


I. 01690 


61.388 


320 




10323 


56 


584 


510 


1.26892 


49.195 


150 


I. 01995 


61.204 


330 




11005 


56 


236 


520 


I 27975 


48.778 


160 


1.02324 


61 .007 


340 




1 1 706 


55 


883 


530 


I . 29080 


48 360 


170 


I .02671 


60.801 


350 




1 243 1 


55 


523 


540 


I . 30204 


47.941 


180 


1.03033 


60.587 


360 




13175 


55 


158 


550 


1-31354 


47.521 


190 


T.03411 


60.366 


370 




13942 


54 


787 








200 


1.03807 


60.136 


380 




14729 


54 


411- 









STEAM AND ITS PROPERTIES. 265 

128. Changes of Physical State from ice to water, or from 
water to steam, or the reverse, are brought about by change of 
temperature and pressure. The heating of ice from any tem- 
perature below freezing up to its melting-point causes an ex- 
pansion of the mass and the conversion of a part of the heat 
supplied in the performance of the work of separation of mole- 
cules, and in less degree that of expansion of the mass against 
atmospheric pressure. At the melting-point rise in tempera- 
ture ceases, and all heat received is transformed into the work 
of " disgregation," as Clausius has called it, until such a separa- 
tion of molecules has been effected that stability of form is 
lost with the vanishing of the visible effect of the polarizing 
forces, and the mass becomes liquid. This change of physical 
condition having been effected, the addition of heat again 
causes rise in temperature, until a second halt takes place at 
the boiling-point and a second change of state produces vapori- 
zation. Above this latter point, the boiling-point, the absorp- 
tion of heat once more causes increase of temperature. There 
are thus two marked phenomena to be noted in applying heat 
to this substance, and at every stage the heat-supply is to be 
observed and compared with the amount of heating and of 
work done internally and externally ; the two quantities, that 
received and the sum of these expenditures, will always be 
found to balance. 

129. The "Critical Point" is that at which the fluid is in- 
differently liquid or vapor at the same temperature and the 
same pressure. As the pressure increases and temperature rises, 
the quantity of heat rendered '' latent" by conversion into the 
work of vaporization decreases, and with probably every fluid 
a point is finally reached at which a critical set of conditions is 
attained, the latent heat of expansion becoming zero, and the 
body exhibiting the properties of the liquid or of the vapor ac- 
cordingly as it is above or below this point on the thermometric 
and pressure scales. M. Cagniard de la Tour in 1822 first ob- 
served that, on raising the temperature of a confined fluid, part- 
ly liquid and partly gaseous, a point might be reached at which 
the whole mass suddenly became homogeneous in appearance ; 
and he supposed the action that of sudden gasification. Fara- 



266 



THE STEAM-BOILER. 



day found, a year later, as he stated it, that, above a certain 
temperature, definite for each case, no amount of pressure would 
cause liquefaction of a vapor ; and Dr. Andrews, who studied 
the phenomenon very carefully, finally concluded that at this 
^' critical " point the properties of the two forms of matter 
blended — that the one passes into the other without interrup- 
tion of continuity ; these physical states being thus found to be 
separate forms of the same condition of matter. M. de la Tour 
reported several critical temperatures and pressures, thus : 





Temperature. 


Pressure 
Atmos. 


Ether 


369^.5 F. 187°. 5 C. 
497°. 5 F. 258^.5 C. 
504°. 5 F. 262°. 5 C. 
773°. oF. 411°. 7 C. 


37-5 

119. 

66.5 


Alcohol 


Carbon disulphide 


Water 







At a temperature and pressure near that above given 
water dissolved glass. Steam in this condition, or of higher 
temperature and pressure, being worked in the steam-engine, 
would superheat while expanding ; at ordinary temperatures 
and pressures, and below this critical state, it partially condenses 
while expanding behind a piston, and thus performing work — 
a fact predicted by Rankine and Clausius in 1849, before its 
experimental discovery. 

Isothermal lines of temperatures considerably above those 
of the critical points for the various pressures are sensibly hy- 
perbolic ; but as these critical pressures and temperatures are 
approached the curve becomes distorted, and gives a combina- 
tion of nearly straight lines up to the boiling-point, a perfectly 
straight line of constant pressure and variable volume during 
vaporization, and finally it is hyperbolic when the gaseous 
state is attained, as in the vaporization of water. 

Fig. 65 exhibits a set of isothermals for carbon dioxide, 
as drawn from Dr. Andrews' data. The dotted lines indicating 
the probable form, as suggested by Professor James Thomson,* 
of portions not obtainable from those data, are by him given the 
Author, as shown. Each curve relates to one temperature, and 

* Rapt. Brit. Assoc. 1S71. 



STEAM AND ITS PROPERTIES. 



267 



pressures are represented by the horizontal ordinates, and cor- 
responding volumes of mass of carbonic acid constant through- 
out all the curves are represented by the vertical ordinates. 




Islol M l.-|;l' I I lap 



Vci I u in. ti 

io|il I I Irlol 1 I Myl 

in ^iuL^s/i/ 



sjol I.I \a\i\ I I I 
Fig. 70.— Isothermal Curves. CO2. 



Thomson points out that, by experiments of Donny, Dufour, 
and others, we have already proof that a continuation of the 
curve for the liquid state past the boiling stage for some dis- 
tance, as shown dotted in Fig. 70, from a to some point ^ 
towards /, would correspond to states already attained. The 
overhanging part of the curve from e to /may represent a state 
in which there would be unstable equilibrium ; and thus, al- 
though the curve there appears to have some important theo- 
retical significance, yet the states represented by its various 
points would be unattainable throughout any ordinary mass of 
the fluid. It seems to represent conditions of coexistent tem- 
perature, pressure, and volume, in which, if all parts of a mass 
of fluid were placed, it would be in equilibrium, but out of 
which it would be led to rush, partly into the rarer state of gas, 
and partly into the denser state of liquid, by the slightest in- 
equality of temperature or of density in any part relatively to 
other parts. Above this point the fluid, as shown by the hy- 



268 THE STEAM-BOILER. 

perbolic form of curve, is \kioxoM^iAy gaseous ; below that point 
it may be called vapor. 

130. The Spheroidal State of water is that condition ob- 
served when water lies in contact with highly heated metal sur- 
faces. When so situated, a Hquid does not wet the metal, but is 
supported quite out of contact with it by a cushion of rapidly 
forming vapor. A very small mass assumes the form of a drop, 
a larger quantity that of a sheet of liquid of continually chang- 
ing outline. The supporting '' Crookes's layer," as it is some- 
times called, consists of particles constantly bounding and re- 
bounding between the adjacent surfaces of fluid and metal, and 
gradually finding their way out of that capillary space as their 
places are taken by newly formed particles of vapor. Ether 
and bromine can be similarly supported on the surface of heated 
water, and ice can be produced in a red-hot crucible without 
contact. On cooling the metal, a temperature is finally reached 
(356° F., 180° C.) at which contact occurs, and an explosion often 
follows from the sudden and considerably increased evolution 
of steam. 

This, which is named, from its discoverer, Leidenfrost's phe- 
nomenon, or, otherwise, the " caloric paradox," has been very 
carefully studied, especially by Boutigny. The temperature of 
the spheroid of liquid is found always to be lower than its boil- 
ing-point ; contact never exists, during the continuance of the 
phenomenon, between metal and liquid. This action is pro- 
moted by any conditions which tend to prevent actual contact 
and wetting of the metal by the liquid, a fact having impor- 
tant bearing on the special danger of certain forms of oily or of 
pulverulent scale in steam-boilers. This interesting and im- 
portant action is illustrated in the impunity with which the hand 
may sometimes be dipped in molten metal, the moisture on its 
surfaces protecting it from contact and injury. 

Superheated water or other liquid may be sometimes ob- 
tained by careful management, as in the experiments of Donny, 
Dufour, and others. When water is deprived of air and of all 
impurities it may be raised to a temperature considerably ex- 
ceeding the boiling-point. The smaller the mass, the higher 
the temperature attainable. M. Donny raised water in a closed 



STEAM AND ITS PROPERTIES. 269 

glass tube to 248° F. (i 38° C), when explosive ebullition occurred, 
and the thermometer dropped to 212° F. (100° C). Minute 
drops (i to 3 mm. or 0.04 to 0.12 in. in diameter) attained 346° 
F: (175° C), when suspended in a mixture of oils of its own den- 
sity, a temperature at which the tension of steam in contact 
with its water is, under normal conditions, between 8^ and 9 
atmospheres. Water in glass vessels always boils, if pure, at 
a temperature slightly exceeding the ordinary boiling-point. 
Larger masses or impure water are not easily superheated. 
M. Dufour found that water retains the liquid state more per- 
sistently when the temperature is constant and pressure is made 
the variable than when the contrary conditions are arranged. 
MM. Donny, Dufour, and others have suggested that this phe- 
nomenon may be a frequent cause of a class of boiler-explosions 
known as " fulminating," in consequence of their violence ; and 
Mr. Radley, an English engineer, reported * having actually su- 
perheated the water in small steam-boilers 27° F. (15° C.) above 
the normal boiling-point for the pressure at which they were 
working. On the other hand, Mons. Hirsch, the well-known 
French engineer and author, reports to the Commission Centrale 
des Machines a Vapeur the results of experiments of a committee 
on the production of the superheated condition in the water of 
steam-boilers, in which, studying the history of such phenomena 
so far as they are recorded, and conducting a somewhat ex- 
tended series of experiments, the conclusion was finally reached 
that there is no evidence, up to the present time, that boiler 
explosions may be caused by the conditions studied, or that 
such conditions ever arise in practice. If they occur at all, it 
is only in extremely rare instances, and as a consequence of a 
coincidence of circumstances seldom to be observed, and which 
are neither well understood nor well defined. The use of the 
thermometer is advised to determine the facts bearing upon 
this question. The commission to which the report is made 
approve and adopt these conclusions. 

131. Vaporization of water or other liquid has been seen to 
be a process of conversion of sensible heat-energy into the so- 



* Lond. Mining Journal, June 28, 1856; Scientific A7ncrican, Aug. 2, 1856. 



270 THE STEAM-BOILER. 

called latent form by transformation into work in the separation 
of molecules, and consequent change of state of the fluid. This 
change has been found to be invariably produced at a tempera- 
ture fixed for every pressure under normal conditions, and to 
demand a certain exact and determinable quantity of heat. 
The vapor thus formed, so long as it is in contact with the 
liquid from which it issued, retains the precise temperature of 
ebullition, and in this condition the steam is said to be satu- 
rated. If it contains no unevaporated moisture, it is said to 
be dry and saturated. It is capable of being superheated by 
isolation and further addition of heat, and then rapidly assumes 
more or less perfectly the gaseous state. M. Hirn found that 
this state is sensibly reached when the superheating amounts 
to anything above 16° F. (9° C). The fluid is known in this 
condition as " steam-gas." 

The specific heat of superheated steam is 0.48, equivalent 
to 371 foot-pounds, at constant pressure, and is 0.37 (286 foot- 
pounds) at constant volume. The quantity of heat doing in- 
ternal work here becomes insensible. The processes of conver- 
sion of the liquid into vapor and of the vapor into gas are seen 
to be, physically, very similar. 

132. The Thermal and Thermodynamic Phenomena 
attending the production, storage, and transfer of heat-energy 
through the vaporization of steam are evidently in some sense 
identical phenomena. The communication of heat to a mass 
of water enclosed in a steam-boiler results in the raising of its 
temperature, the expansion of the mass, the performance of 
work, and the conversion of heat-energy in the doing of that 
work. The boiling-point is simply a point in the process at 
which the proportion in which the heat received is distributed 
to its several purposes is altered, and the superheating of steam 
is the result of passing another critical period in the process. 
The principles involved and these phenomena have been 
already fully explained, and it is only necessary here to apply 
those principles and the data obtained by experiment to the 
special case in hand — the production and use of steam. It is 
perfectly easy to determine just how much sensible heat is em- 
ployed, untransformed, in raising the temperature of water or 



STEAM AND ITS PROPERTIES. 27 1 

steam ; how much is transformed in producing expansion, and 
how much as the latent heat of change of state. 

133. Internal Pressure and Work, in the case of steam, 
will illustrate the general case of thermodynamic change as 
already presented. The magnitude of the molecular resistance 
to expansion is well ascertained, and the quantity of work done 
in overcoming them in the process of making steam is as easily 
determinable. As has been shown, the quantity of heat be- 
coming latent is the equivalent of this internal work, and the 
sum of the latent and the sensible heat absorbed is the total 
heat demanded to produce the change. Both may be deter- 
mined by the processes which have been described in the 
earlier chapters. 

134. The Computation of Internal Work or of internal 
pressure has been seen to be based on the principle expressed 
in the statement of the second law of thermodynamics. 

The total pressure, internal and external, at any tempera- 
ture, T, is always 

p=^%-- • • w 

dp 
The rate of variation, -^, of pressure as a function of tem- 
perature is determined experimentally, and the value of this 
expression may be obtained from the expressions already given, 
or from the tables of Regnault. The work done is the product 
of their total pressure, /, into the alteration of volume, Av^ or 

W = pAv=T-^Av (2) 

Internal pressure and work are completed by deducting exter- 
nal pressure and work from these totals. 

Clausius thus obtained the following values oi p for steam 
of the pressures given, all in millimetres of mercury, of which 
760 measure one atmosphere of pressure : 



2/2 



THE STEAM-BOILER. 
TOTAL PRESSURES OF STEAM. 



Centigrade. 


External Pressure. 


Ratio 


Total Pressure 


Ratio 








dp 


^-If 


L 








/. 


T. 


A. 


At. 


dT' 


/e 


IOO° 


374° 


760 


I 


27.200 


IOI46 


13-3 


120 


394 


1520 


2 


48. 595 


19150 


12.6 


134 


408 


2280 


3 


67.020 


27277 


11.9 


144 


418 


3040 


4 


84.345 


35172 


Il-i 


152 


426 


3S0O 


5 


100.375 


42659 


II. 2 


159 


433 


4560 


6 


116.085 


50149 


II. 


166 


440 


5320 


7 


133-445 


58502 


10.8 


171 


445 


6080 


8 


146.910 


65228 


10.7 


176 


450 


6840 


Q 


161.27 


72410 


10.6 


180 


454 


7600 


10 


173.425 


78561 


10.4 


199 


473 


1 1400 


15 


239-57 


II3077 


9-9 



It is seen that the rate of variation of pressure with the 
temperature of steam continually increases as pressures and 
temperatures rise, and that the proportion of internal to ex- 
ternal work and pressure continually diminishes ; but that the 
latter ratio is large, about ten to one, for the whole range of 
pressures familiar in standard practice. 

135. The Specific Volume of steam, or the volume of 
unity of weight, and its reciprocal, the density, have been seen 
to be capable of easy computation when the latent heat of 
vaporization at the given temperature is known ; since this 
latent heat measures the work done while the force resisting it 
is calculable as above. From the expressions already given 

dp ^ ^ H dp 



H=T^Av; Av = 



we thus obtain very exact values. 

Clausius thus obtains the following values, and compares 
them with the somewhat uncertain figures of Fairbairn and 
Tate, derived experimentally. Metric m easures are employed. 



i. 


T. 


A7' 

Calculated. 


A.. 
By Experiment. 


II7-I7 
124.17 
128.41 
137-46 
144-74 


391-17 
398-17 
402.41 
411.46 
418.74 


0.947 
0.769 
0.681 
0.530 
0.437 


0.941 
0.758 
0.648 
0.514 
0.432 



STEAM AND ITS PROPERTIES. 



273 



Quite accurate results can also be obtained by taking the 
density of steam as 0.622 ; that of air at the same values of t 
and/ being unity. 

' The volume of water increases with temperature, from the 
temperature of maximum density, more and more rapidly as 
the heat is increased. The following are the values as given 
by M. Kopp, who experimentally determined them, and as cor- 
rected by Mr. Porter to make the curve exhibiting the data 
perfectly smooth : 



Tem 


PERATURE. 


Volumes as per 


Cent. 


Fahr. 


Kopp. 


Poiter. 


4° 


39° -I 


I . 00000 


I . 00000 


5 


41 .0 


I. 0000 I 


I. 0000 I 


10 


50 .0 


1.00025 


I .00025 


20 


68 .0 


I. 00169 


I .00171 


30 


86 .0 


1.00423 


1.00425 


40 


104 .0 


1.00768 


1.00767 


50 


122 .0 


I.OII90 


I.011S6 


60 


140 .0 


I. 01672 


I. 01678 


70 


158 .0 


T.0223S 


I. 02241 


80 


176 .0 


I. 02871 


I .02S72 


90 


194 .0 


1.03553 


1-03570 


100 


212 .0 


I. 04312 


1.04332 



136. Temperature, Pressures, and Volumes of Steam 

are related by natural law quite as definitely as those governing 
these relations for the gases ; but algebraic expressions of those 
laws are not yet obtained, except empirically. There have been 
numerous formulas proposed of the latter class, some of which 
are remarkably exact within a moderate range. The most ac- 
curate are probably those of Rankine,^ already given for vapors 
generally : 

/? C 
\ogp = A--^--^,; (r) 



y 



A - log / 
C 



+ 






-1- 

2CJ' 



(2) 



* Steam-engine, p. 237, §206. Ibid., pp. 559-564, 



18 



274 THE STEAM-BOILER. 

in which, for steam, 

■n 

A = 8.2591 ; ^r= 0.003441; 



log B = 3.43642 ; 

log C = 5-59873 ; T^i = o.ooooi 184 ; 



pressures being taken in pounds on the square foot and tem- 
perature in degrees Fahrenheit on the absolute scale. The ex- 
periments of Regnault and of Fairbairn and Tate have furnished 
the generally accepted values. 

Unwin has proposed ^' a simpler formula than Rankine's, 
which, while not quite as exact, gives more manageable ex- 

pressions for -7^ and its functions ; thus, for vapors generally : 
log/ = ^-y-,-; (3) 



^=[^-)"-' (4) 



I dp nb 

-^ = 2.3025-^.^ 

n-\-x 

(a — log pY~^~ , , 

= 2.3025;^^ ^f^ ;. ... (5) 

b » 



t dp nb 

-^- = 2.3025^^- 

= 2.io2^n{a — log p) (6) 

* Phil. Mag., April, 1886. 



STEAM AND ITS PROPERTIES 2/5 

For steam, these formulas become : 

(7) 

(8) 



log/ = 7.5030 --p^^; . . , 


• • t 


2^_f 7579 Y\ 




V.5030-log// ' 


• • • 


I dp 21815 
pdT~ r--5 

_ (7-5030- log /)-8^ 
441.3 


► • • 


T dp 21815 
p dT ~ Z^ -5 





(9) 



= 2.8782(7.5030- log/); . . .(10) 

which expressions give remarkably exact results. Metric meas- 
ures are used throughout. 

137. The Specific Heats of Water and Steam vary 
somewhat with temperature ; this variation is noted with all 
solids, and occurs with the vapors, although in vastly less de- 
gree ; and this is one point in which they are distinguished from 
the gases. For all the purposes of the engineer the specific 
heat of either saturated steam or of steam-gas may be taken at 
the value obtained by Regnault, 0.305, the quantity of heat, in 
thermal units, demanded to raise the temperature of unity of 
weight of saturated steam one degree, while still keeping it 
saturated by the evaporation of additional water ; which latter 
process demands the transformation of 0.695 unit of heat. 

The specific heat of isolated steam-gas, or superheated 
steam, is given by Regnault as 0.48051, and constant. 

The specific heat of water was determined by Regnault* 
very carefully and exactly, and the figures so obtained have been 

*Mem. of the Academy of Sciences, 1847. 



2/6 THE STEAM-BOILER. 

found capable of being very accurately represented by the fol- 
lowing empirical formula of Rankine :^ 

6^= I +o.oooooo309(/ — 39°.i)', . . . . (i) 

in which t is the temperature on the common Fahrenheit scale. 
The total heat demanded from t^ to t^ would thus be 

h = J ^Cdt = t^ — t^-\- 0.000000 1 03 [(^2 — 39°. i)' 

-(^:-39°.i)1;. . (2) 

and the mean specific heat for such a range of temperature is 

j—^^ = i+o.ooooooi03[(4-39°-i)'+(^.-39°-i)(A-39°-i) 

+ (A-39°.iy].. • (3) 

On the Centigrade scale these expressions become 

C=. I +0.00000 1 (/— 4°)', . (id) 

h = /,-/,+o.oooooo33[(^,- 4°)'- (A- 4°)1, . . . (2^) 

~j^ = I + oooooo33[(^. - 4°)^ + {h - 4°)(^x - 4°) 

+ (^.-47] (3^) 

The specific heat of ice is given by M. Person as 0.504. 

138. The Computation of Latent and Total Heat of 
Steam is readily made by means of formulas given by Reg- 
nault or based upon his work, which covered a wide range of 
temperature — from a little below the freezing-point to about 
375° F. (190° C). The following is the formula of Regnault 
for latent heat as slightly modified and corrected by Rankine 
for the British and metric systems, respectively : 

/ = 1091.7 — o.695(^ — 32°) — o.ooooooio3(/ — 39°. i)' ; . (i) 
4 = 606.5 — 0.695 / — o.oooooo333(^ — 4°)' ; . . . . . (i^) 



* Trans. Royal Soc. of Edinburgh, 1851; Steam Engine, p. 246. 



STEAM AND ITS PROPERTIES, 277 

or, approximately, as given by the investigator, 

/ = 1092 - o.7{t - 32°) 

= 966 — o7(/ — 212) 

= 1147-07/ (2) 

l^— 606 — 0.7/ (2a) 

The total heat of evaporation is the sum of the latent and 
sensible heats, and may be taken as 

h = C{t,-t,) + l, 

= i09i.7 + a305(/-32°); . . , ., (3) 
7^,^=606.5+0.305/;. ..... . .(3^) 

in which the " total heat " measured is that /ro7n t^ at t^, the 
original temperature of the water and that of evaporation, and 
the formulas given being based on the assumption that /^ is 
taken at the melting-point of ice. For any other temperature 
the following will give satisfactorily exact measures: - 

k = 1092 + o.3(/, - 32) - (/, - 32°) ; 

= ii46 + o.3(/,-2i2)-(/,- 32°); . . . (4) 
A,n= 606.5+0.3/, — /, ; . . . .... . (4^) 

k being obtained in British measures and /i^ in metric. 
For steam-gas^ 

h = 1092 + o.48(/, — /,) (5) 

.. Professor Unwin proposes the following for the latent heat 
of vaporization of steam : 

4 - 799 - ^^ 5030 _ lQg^)o.8 , (6) 

which is found to be extremely exact. He also obtains for the 
expansion during change of state, 

^'^•"=-«-/W^i^^ (7> 

/ being expressed, as above, in millimetres of mercury. 



2^^^ 



THE STEAM-BOILER, 



139. Factors of Evaporation measure the relative amount 
of heat demanded to effect the heating of water from a given 
temperature, t^, and its vaporization at a higher temperature, 
/j, and to simply produce vaporization at the boiling-point un- 
der atmospheric pressure, which latter is now usually taken as a 
standard. The value of this factor of evaporation is evidently 



f^^-^ 



0.3(/.-2I2°)+(2I2°^0 
966.1 



nearly. . (i) 



The following are values of such factors, calculated as 
above : 





TABLE OF 


FACTORS 


OF EVAPORATION. 














Initial Temperature of 


Feed 


-WATER, T'q. 






Boiling-point, Ty. 






















Fahr. 


























32° 


50° 


68° 


86° 


104° 


122° 


140° 


158° 


176° 


194° 


2I2» 


212° 


1. 19 


1. 17 


1. 15 


I-I3 




1. 10 


1.08 


1.06 


1.04 


1.02 


1. 00 


230 


1.20 


1. 18 


1. 16 


1. 14 


1. 12 


1. 10 


1.08 




06 


1.04 


1.02 


1. 01 


248 


1.20 


1. 18 


1. 16 


1. 14 


1 .13 


I. II 


1.09 




07 


1.05 


1.03 


1. 01 


266 


1. 21 


1.19 


1. 17 


1-15 




I. II 


1.09 




07 


1.06 


1.04 


1.02 


284 


1. 21 


1.20 


1.18 


1. 16 




1. 12 


1. 10 




08 


1.06 


1.04 


1.02 


302 


1.22 


1.20 


1. 18 


1. 16 




1. 12 


I. II 




09 


1.07 


1.05 


1.03 


320 


1.22 


1. 21 


1. 19 


1. 17 




113 


I. II 




09 


1.07 


1.05 


1.03 


■ 338 


1.23 


1. 21 


1. 19 


1. 17 




1. 14 


1. 12 




10 


1.08 


1.06 


1.04 


356 


1.23 


T.22 


1.20 


1. 18 


1. 16 


1. 14 


1. 12 




10 


1.08 


1.06 


1.04 


374 


1.24 


1.22 


1.20 


1. 18 


1. 17 


1-15 


I-I3 




II 


1.09 


1.07 


1.05 


392 


1.24 


1.23 


1. 21 


1. 19 




I-I5 


I-I3 




II 


1.09 


1 07 


1.06 


410 


1.25 


1.23 


1.22 


1.20 


1. 18 


1. 16 


1. 14 




12 


1. 10 


1.08 


1.06 


428 


1.25 


1.24 


1.22 


1.20 


...» 


1. 16 


1. 14 




12 


I. II 


1.09 


1.07 



A vastly more convenient form of table is that in which the 
pressures at which evaporation takes place are given ; thus ; 



STEAM AND ITS PROPERTIES. 



279 





i 


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IN 


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280 7'HE STEAM-BOILER. 

It is seen that the relative cost of using feed-water at any- 
one temperature as compared with the use of water at any 
other temperature is as the reciprocal of their factors of evapo- 
rization. Thus if feed-water can be supplied, by means of a 
heater, at 210° F., where previously drawn from the mains at 
50°, the relative cost of making steam will be, at 100 pounds 
pressure, by gauge, \%^ = 0.86, and a gain of fourteen per 
cent will be effected. As will be seen later, these tables are 
very useful in reducing the data obtained in trials of steam- 
boilers to the standard. 

140. Regnault's Researches and Methods have furnished 
all the essential data relating to the production of steam in the 
boiler and the supply of stored heat-energy to the engine. 

The memoir of M. Henri Victor Regnault on " The Elastic 
Forces of Aqueous Vapors," * in which he described his re- 
searches, is a most magnificent exposition of a still more re- 
markable series of investigations. He repeated the methods 
and experiments of earlier physicists, invented new ways, and 
finally obtained a set of data of unexampled extent and accu- 
racy.f Regnault found that the density of aqueous vapor in 
vacuo and under feeble pressure may be calculated according to 
the law of Boyle and Marriotte when the fraction of saturation 
is less than 0.8, while the density becomes sensibly greater 
when approaching saturation. He further found that the den- 
sity of vapor ill air, in a state of saturation, may be similarly 
calculated, and the ratio of weight of equal volumes of vapor 
and air is a trifle less than that obtained theoretically. 

The data obtained by Regnault were carefully tabulated, 
and curves were constructed exhibiting the variation of pres- 
sure with temperature for saturated steam for the whole range 
covered by his experiments. Three formulas of interpolation 
were used for three different parts of the scale of temperatures ; 
for that part below the freezing-point he adopted the formula 

F=a^ba% (I) 

^ Ann. de Chimie et de Physique, July, 1844 ; Mem. de I'lnstitut, tome xxi., 
p. 465 (1847) ; Mem. de I'Academie des Sciences, xxi, xxvi. 
f Vide Dixon on Heat, vol. i., § 724. 



STEAM A AW ITS PROPERTIES. 28 1 

in which F is the pressure, a and b constants, and a'' a function 
oi r = t-{- 32°, t being the temperature corresponding to F. 

Between the freezing and boiling points Regnault used 
Biot's formula, 

\ogF=a + ba'-cfi*\ (2) 

and above the boiling-point, 

\og F — a — ba!" — eft'' \ ...... (3) 

in which r = / + 20. This last answers well, also, for the whole 
range. In it ^2: = 6.2640348 ; log ^ = 0.1397743; log c = 
0.6924351 ; log a — 1.994049292; log ^— 1.998343862, as given 
by Regnault ; or, according to Dixon, 

a — 6.263 509 ^'^^ 5 
log^ = i. 998 343 377 8 
log^ = f.994 048 173 7 
log b — 0.692 450 419 2 
log^ = 0.139 553 958 4 



For British measures 



a = 4.859 984 524 7 

log a = 1.999 079 751 3 

log /3 = f .996 693 778 3 

log^ = 0.659 317 975 2 

log c = 0.020 517 432 4 

A break was observed by Regnault, and is exhibited by the 
curves and the formulas, at the freezing-point, which had been 
attributed to error, the tw^o curves cutting each other at a very 
small but appreciable angle ; but Professor James Thomson 
has supposed such a break to have a real existence, and to be 
produced by the physical change marking the freezing-point. 

141. Regnault's Tables have been reproduced in many 
forms, usually with additions. The Appendix, among other 
tables, contains the data obtained by Regnault (Table I.), and 



282 THE STEAM-BOILER. 

these values are accepted as standard universally. The table 
here given exhibits the temperatures and corresponding pres- 
sures of saturated steam throughout the full range now used 
in steam-boilers and far beyorid ; the quantity of heat, sensible 
and latent, in unity of weight ; the total heat of evaporation, 
and the density of the steam. Reference to these tables is 
vastly more convenient than calculation. Should it be neces- 
sary, or desirable, however, to make such calculations, the for- 
mulas already given will furnish the means. They also permit 
the calculation of data beyond the limits of Regnault's experi- 
ment, and are probably practically correct far beyond any pres- 
sure likely to become familiar in the operation of steam-boilers. 
Regnault's limit was at 230° C. (446° F.). Rankine's formula 
has been used beyond it. 

The formulas used in these calculations are elsewhere given, 
but are here grouped for convenience of reference. British 
measures are used throughout. 



STEAM AND ITS PROPERTIES. 



283 























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284 



THE STEAM-BOILER, 















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STEAM AND ITS PROPERTIES. 285 

142. The Stored Energy in Steam at any pressure and 
temperature is now easily ascertained by calculation, in accord- 
ance with the first law of thermodynamics. 

The first attempt to calculate the amount of energy latent 
in the water contained in steam-boilers, and capable of greater 
or less utilization in expansion by explosion, was made by Mr. 
George Biddle Airy,"^ the Astronomer Royal of Great Britain, 
in the year 1863, and by the late Professor Rankinef at about 
the same time. 

Approximate empirical expressions are given by the latter 
for the calculation of the energy and of the ultimate volumes 
assumed by unit weight of water during expansion, as follows, 
in British and* in metric measures : 

T7 - 77AT-2i2f _ 423-55(^-iooV 

^- r+ 1 134.4 ' "~ r+648 ' 

1/ _ 3^76(7^-212) _ 2.2g{T- 100) 

^ - r+1134.4 ' "~ r+648 

These formulas give the energy in foot-pounds and kilo- 
grammetres, and the volumes in cubic feet and cubic metres. 
They may be used for temperatures not found in the tables to 
be given, but, in view of the completeness of the latter, it will 
probably be seldom necessary for the engineer to resort to 
them. 

The quantity of work and of energy which may be liberated 
by the explosion, or utilized by the expansion, of a mass of 
mingled steam and water has been shown by Rankine and by 
Clausius, who determined this quantity almost simultaneously, 
to be easily expressed in terms of the two temperatures be- 
tween which the expansion takes place. 

When a mass of steam, originally dry, but saturated, so 
expands from an initial absolute temperature, T^, to a final 
absolute temperature, T^^, if^is the mechanical equivalent of 
the unit of heat, and H is the measure, in the same units, of 

* ' ' Numerical Expression of the Destructive Energy in the Explosions of 
Steam Boilers." 

I " On the Expansive Energy of Heated Water." 



286 THE STEAM-BOILER. 

the latent heat per unit of weight of steam, the total quantity 
of energy exerted against the piston of a non-condensing en- 
gine, by unity of weight of the expanding mass, is, as a maxi- 
mum, 

iT T\ T -T 

£^ = /7^.(-^^-i-hyp log-^J + -^^^/^. . . (A) 



This equation was published by Rankine a generation ago.* 
When a mingled mass of steam and water similarly ex- 
pands, if M represents the weight of the total mass and m is 
the weight of steam alone, the work done by such expansion 
will be measured by the expression, 



U= MJtJ^~ _ I _ hyp log ^i) + m ^' ^ ^' H. (B) 



This equation was published by Clausius in substantially 
this form.f 

It is evident that the latent heat of the quantity m, which 
is represented by inH, becomes zero when the mass consists 
solely of water, and that the first term of the second member 
of the equation measures the amount of energy of heated wa- 
ter which may be set free, or converted into mechanical energy 
by explosion. The available energy of heated water, when 
explosion occurs, is thus easily measurable. 

The computers of the tables given in the Appendix 
were Messrs. Ernest H. Foster, and Kenneth Torrance. 
The tables range from 20 pounds per square inch (1.4 kgs. per 
sq. cm.) up to 100,000 pounds per square inch (7030.83 kgs. 
persq. cm.), the maximum probably falling far beyond the range 
of possible application, its temperature exceeding that at which 
the metals retain their tenacity, and in some cases exceeding 
their melting-points. These high figures are not to be taken 



* Steam-engine and Prime Movers, p. 387. 

f Mechanical Theory of Heat, Browne's translation, p. 283. 



STEAM AND ITS PROPERTIES. 287 

as exact. The relation of temperature to pressure is obtained 
by the use of Rankine's equation, of which it can only be said 
that it is wonderfully exact throughout the range of pressures 
within which experiment has extended, and within which it 
can be verified. The values estimated and tabulated are prob- 
ably quite exact enough for the present purposes of even the 
military engineer and ordnance officer. The form of the equa- 
tion, and of the curve representing the law of variation of 
pressure with temperature, indicates that, if exact at the 
famihar pressures and temperatures, it is not likely to be in- 
exact at higher pressures. The curve at its upper extremity 
becomes nearly rectilinear. 

The table presents the values of the pressures in pounds 
per square inch above a vacuum, the corresponding reading of 
the steam-gauge (allowing a barometric pressure of 14.7 pounds 
per square inch), the same pressures reckoned in atmospheres, 
the corresponding temperatures as given by the Centigrade 
and the Fahrenheit thermometers, and as reckoned both from 
the usual and the absolute zeros. The amount of the available 
stored energy of a unit weight of water, of the latent heat in a 
unit weight of steam, and the total available heat-energy of 
the steam, are given for each of the stated temperatures and 
pressures throughout the whole range in British measures, 
atmospheric pressures being assumed to limit expansion. The 
values of the latent heats are taken from Regnault, for mode- 
rate pressures, and are calculated for the higher pressures, be- 
yond the range of experiment, by the use of Rankine's modifi- 
cation of Regnault's formula. 

Studying the table, the most remarkable fact noted at the 
lower pressures is the enormous difference in the amounts of 
energy, in available form, contained in the water and in the 
steam, and between the energy of sensible heat and that of 
latent heat, the sum of which constitutes the total energy of 
the steam. At 20 pounds per square inch above zero (1.36 
atmos.), the water contains but 145.9 foot-pounds per pound ; 
while the latent heat is equivalent to 16,872.9 foot-pounds, or 
more than 115 times as much; i.e., the steam contains 116 
times as much energy in the form of latent heat per pound, as 



288 THE STEAM-BOILER. 

does the water, from which it is formed, at the same tempera- 
ture. The temperature is low ; but the amount of energy ex- 
pended in the production of the molecular change resulting in 
the conversion of the water into steam is very great, in conse- 
quence of the enormous expansion then taking place. At 50 
pounds the ratio is 20 to i ; at 100 pounds per square inch it 
is 14 to I, at 500 it is 5 to I ; while at 5000 pounds the energy 
of latent heat is but 1.4 that of the sensible heat. The two 
quantities become equal at about 7500 pounds. At the high- 
est temperature and pressure tabled, the same law would make 
the latent heat negative ; it is of course uncertain what is the 
fact at that point. 

At 50 pounds per square inch the energy of heated water 
is 2550.4 foot-pounds, while that of the steam is 68,184, or 
enough to raise its own weight to a height, respectively, of a 
half-mile and of 12 miles. At 75 pounds the figures are 4816 
and 90,739, or equivalent to the work demanded to raise the 
unit weight to a height of four fifths, and of about 17 miles re- 
spectively. At 100 pounds the heights are over one mile for 
the water and above 20 miles for the steam. 

Comparing the energy of water and of steam in the steam- 
boiler with that of gunpowder, as used in ordnance, it will be 
found that at high pressures the former become possible rivals 
of the latter. The energy of gunpowder is somewhat variable 
with composition and perfection of manufacture, and is very 
variable in actual use, in consequence of the losses in ordnance 
due to leakage, failure of combustion, or retarded combustion 
in the gun. Taking its value at what the Author would con- 
sider a fair figure, 250,000 foot-pounds per pound, it is seen 
that, as found by Airy, a cubic foot of heated water, under a 
pressure of 60 or 70 pounds per square inch, has about the same 
energy as one pound of gunpowder. The gunpowder ex- 
ploded has energy sufficient to raise its own weight to a height 
of nearly 50 miles, while the w^ater has enough to raise its 
weight about one sixtieth that height. At a low red heat wa- 
ter has about 40 times this latter amount of energy in a form 
to be so expended. One pound of steam, at 60 pounds pres- 
sure, has about one third the energy of a pound of gunpowder. 



STEAM AXD ITS PROPERTIES. 



289 



At 100 pounds it has as much energy as two fifths of a pound 

of powder, and at higher pressures its energy increases very slowly. 

143. The Curves of Stored Energy are most instructive. 

Plotting the tabulated figures and determining the form of the 



1 Til 1 i 1 ' ' 1 -^ ^Nh a a 


T Till ' 'T r ' " ' i_ xrL 


iL lU_,_ . J Vu"' " 1 -+-'-+- 


T hi't" lir 1 L " ' ' ^aX- 


,«v, " ' 1 in h ~! H -xv ' ^^ ' - --It 


!«»-- -" j- i ■ !' "I — r ■'■ -■■- -- - -- icii ^r 


■ 1 ■ 1" [" '! ! i ■'■ -\"-\- T[ it 




T t'""' " 1"" n "T "^ ..... i -it- L 






it Ul - = ql 


"^ ' T -5^ - 


- ~- X _t--<^i- - - - 


linn 1 , ' <rrsF'°'^ - 


^^ - ... , ^^^j^ i y- 


XS^cS^jT 


it ^ ^==^^- ^2. r . . _t _ 


" •" ^^?aUH^ 1 


,onn ' iL^3^E!l _ _:: 


jsoo--- ^-, -- ^^-/y^vti-- - 


" J "^ ! 1 f~ 1 r ^ =^=•'^^' 1 , ■ - 


i \ ' '-^ A^ \ -\- f r- _ _ 


- ■ -y r LL<i<kaj 1 JIL- J 


,,„ - -- -t -t>-c^'J^f -til hi 


^^ it ..>41 J i_r""j_i|_L ' 1 _ 


it ^^zt^^ ' Jlt ic < TH - _ _ . _ 


"17/ 1 >" 1 n~i ! I , ' ■ -- 




•' 1 1 >^ . i 1 ' , i 1 M ^.11 


uoo - \ ' y i ' ) 1 ~^. --,--■■■- ■ i 1 1 ' , 1 1 


" T -yf i 1 t . 1 1 i 1 I 1 


-t "' ■j'f '■ i i ' , ' 1 1 ■ - ■ 


yr-T -•■! , 1 ' 1 1 ■ -. 


lom " " ■ ^M ' i 1 1 1 M ' M 


'"" / ' 1 ' i Ml 1 ■ - 


-■" / -i 1 i M 1 ' .. _ _lt 


"1 TT rri ■ I'! 1 1 ' \ 


T ! i/l 1 , ! 1 i! i i M 5 , 1 ! 


niann 1 ' /l 'i T ' . 1 ' , 1 


5)900 i/ 1. ! 1 ' 


H V;7t FT T^ 1 ' 


v^ (_- . . . 


C 41- ^.-J---- ... -^- 


qonn 1\ ■" 'l' i M 1 1 


H800 ■w-r 1 "i" 'M i 1 


• -\i ; 1 1 i III i 


! 1 > |! 1 1 1 1 i 1 1 . i ..... 




-fu. i Vi 1 ' ' 'I'M 


700 - X, 1 1 


- >J ■ j 




^s J _i_ 4_ __ 






1 - -^sZ _ ::: 


. X ^^K 


" ± ^>^_ - - X ■ — 


nvi ' 1 <?rN-L 


1 fr^JJJ 1 1 




i ' ^ ft? ■"-. 


i 1 ' "^ i " >:^>.. 




400 --M ) i ; ^^WT,^^^ -- 


M 1 < 1 M 1 -- - '"-rf-k^z 


M 1 ' j [ 1 . , . . , ^ *■ »? ' ^ K " " 




•mr li 1 : M j '■■^■. 


SOC ! j ■ ■■^ 


1 1 1 1 i 




1 1 i 1 ■ 1 1 ' ■ ■ - 


am M Ml ^ 


SCO , ! 




i I 










■ 1 1 1 


. 1 1 1 1 





IJOff* 



80(f 



lUW 20U0 3000 4000 eOOO 6000 rmi 8000 9000 10000 UOUO 12000 



Fig. 71. — Curve of Heat ix Steam. 

curve representing the law of variation of each set, we obtain 
the peculiar set of diagrams exhibited in the accompanying en- 
graving. In Fig. 71 are seen the curves of absolute tempera- 

IQ 



290 



THE STEAM-BOILER. 



ture and of latent heat as varying with variation of pressure. 
They are smooth and beautifully formed lines, having no rela- 
tion to any of the familiar curves of the text-books on co-ordi- 




2000 



8000 4000 5000 6000 7000 

ABSOLUTE PRESSURE IN FOOT POUNDS PER. SQ. IN. 

Fig. 72 — Curve of Heat-energy in Steam. 



nate geometry. In Fig. 72 are given the curves of available 
energy of the water of latent heat and of steam. The first 
and third have evident kinship with the two curves given in 



STEAM AND ITS PROPERTIES. 29 1 

the preceding illustration ; but the curve of energy of latent 
heat is of an entirely different kind, and is not only peculiar in 
its variation in radius of curvature, but also in the fact of pre- 
senting a maximum ordinate at an early point in its course. 
This maximum is found at a pressure of about one ton per 
square inch — a pressure easily attainable by the engineer. 

Examining the equations of those curves, it is seen that 
they have no relation to the conic sections, and that the curve, 
the peculiarities of which are here noted, is symmetrical about 
one of its abscissas, and that it must have, if the expression 
holds for such pressures, another point of contrary flexure at 
some enormously high pressure and temperature. The for- 
mula is not, however, a " rational " one, and it is by no means 
certain that the curve is of the character indicated ; although 
it is exceedingly probable that it may be. The presence of 
this characteristic point, should experiment finally confirm the 
deduction here made, will be likely to prove interesting, and 
it may be important ; its discovery may possibly prove to be 
useful. 

The curve of energy of steam is simply the curve obtained 
by the superposition of one of the two preceding curves upon 
the other. It rises rapidly at first, with increase of tempera- 
ture, then gradually rises more slowly, turning gracefully to 
the right, and finally becoming nearly rectilinear. The curve 
of available energy, of heated water, exhibits similar character- 
istics ; but its curvature is more gradual and more uniform. 

144. The Actual Power of Steam and of Boilers evi- 
dently depends upon the efficiency of the method of applica- 
tion, and on the apparatus employed. The quantity of heat- 
energy supplied to the engine and yielded by the generator 
has been seen to be easily calculable by simply multiplying the 
quantity of heat given to the steam by the fuel, by the me- 
chanical equivalent of heat. The amount available as energy 
may be the total quantity so supplied, as when the steam is 
condensed in heating buildings or otherwise, and is returned as 
feed-water to the boilers ; or it may be any less amount, ac- 
cordingly as the method of utihzation is more or less effective. 
The tables given in the Appendix furnish the data for calcu- 



292 THE STEAM-BOILER. 

lation in any case in which the efficiency of transfer and of 
transformation is known. Where no constant value can be 
assumed for the efficiency of the system employed, it is some- 
times, nevertheless, found to be important to establish a stand- 
ard conventionally. Thus, in the calculation of available 
stored energy, as given in the Appendix, Table II., it was as- 
sumed that the steam would be expanded to atmospheric pres- 
sure. Similarly, convention has estabhshed the unit horse- 
power of steam-boilers, in order to afford a standard of 
comparison in test-trials, and to give a means of rating boilers 
by the designer, the builder, or the purchaser and user. 

The operation of boilers occurs under a wide range of 
actual conditions — the steam-pressure, the temperature of feed- 
water, the rate of combustion and of evaporation, and, in fact, 
every other variable condition, differing in any two trials to 
such an extent that direct comparison of the totals obtained, 
as a matter of information regarding the relative value of the 
boilers, or of the fuel used, becomes out of the question. It 
has hence gradually come to be the custom to reduce all results 
to the common standard of weight of water evaporated by the 
unit-weight of fuel, the evaporation being considered to have 
taken place at mean atmospheric pressure, and at the tempera- 
ture due that pressure, the feed-water being also assumed to 
have been supplied at the same temperature. This, in techni- 
cal language, is said to be the " equivalent evaporation from 
and at the boiling-point" (212° Fahr., 100° C). This standard 
has now become generally .incorporated into the science and 
the practice of steam-engineering. The '' Unit of Evaporation " 
is one pound of water at the boiling-point, evaporated into 
steam of the same temperature. This is equivalent to the 
utilization of 965.7 British thermal units per pound of water so 
evaporated. The economy of the boiler may thus be expressed 
by the number of units of evaporation obtained per pound of 
combustible. 

145. The Horse-power of Steam-Boilers must always be 
reckoned on an assumed basis involving the amount of heat 
supplied from the furnace, the conditions determining the 
availability of that heat as stored, and the circumstances con- 



STEAM AND ITS PROPERTIES. 293 

trolling its expenditure and transformation. The term must 
evidently be purely conventional and technical, and its defini- 
tion must be strictly limited. 

The character and magnitude of the unit to be chosen to 
express the " power " of the steam-boiler is not fully settled, 
though the subject has attracted much attention among engi- 
neers. It is evident that since the boiler is merely an appara- 
tus for the generation of steam, and since the province of the 
steam-engine is to develop power from that steam, and with a 
degree of efficiency which may vary enormously, it is certain 
that we have no natural unit of power for steam-boilers. It 
may even be asserted that no natural unit can exist. The 
most scientific system of power-rating yet proposed considers 
the power of a boiler to be that expended by it in driving out 
all the steam which it makes against the pressure of the atmos- 
phere, a system suggested by Nystrom."^ 

The weight of water to be evaporated per hour at any 
given pressure to produce one horse-power as the equivalent of 
its natural effect without expansion, by impelling a piston 
against its load, is calculable with sufficient accuracy by the 
formula of Nystrom : 

13748.4 ^ ^ 

in which Fis the volume of steam^in cubic feet,/ the absolute 
pressure in pounds per square inch, and v the volume of steam 
relatively to that of water at the freezing-point. By this 
method we obtain the following values : 

* Mechanics, i8th Ed., p. 562. 



294 



THE STEAM-BOILER. 



p 


H. P. per Cu. Ft. 


Lbs. per H. P. 


5 


I . 6600 


29.852 


lO 


1-7253 


28.723 


14.7 


I -7540 


28.252 


25 


1.7879 


27.717 


40 


1.8238 


27.170 


60 


I . 8649 


26.573 


80 


I -9033 


26.038 


100 


1.9406 


25.537 


125 


1.9865 


24.945 


150 


2.0321 


24.387 



What is sometimes called the "boiler-heat horse-power"* 
is the power corresponding to the energy imparted to the 
steam by its evaporation within the boiler. This power is 
measured by dividing the weight of steam made by that re- 
quired to produce unity of power, and the latter quantity is 
obtained by dividing the energy in foot-pounds of one horse- 
power per hour by the mechanical equivalent of the latent 
heat of steam ; i.e., 



w 



i,98o,cx)0 
966 X JT^ 



= 2.65 lbs. 



Taking as a standard the quantity of steam demanded by a 
perfect engine, having no clearance, receiving steam at boiler- 
pressure, and expanding it down to a perfect vacuum, or to the 
atmospheric pressure, we may readily obtain figures for the 
weights demanded by which to rate steam-boilers, should it be 
found necessary to resort to such an ideal system. For such 
cases, Zeuner'sf figures are as below: 



* " Boiler-power and Boiler-heating Surface," by Professor R. H. Smith, In- 
dustries, July I, 1887. 
f Warme Theorie. 



STEAM AND ITS PROPERTIES. 



295 





Water per Horse-power per Hour. 


Pressure 


Non-condensing- Engine. 


Condensir 


g Engine. 


AjMOSPHERES. 










Lbs. 


Kilogs. 


Lbs. 


Kilogs. 


3 


33 


I5i 


13 


6 


4 


26 


12 


12 


5i 


5 


23 


loi 


Hi 


5i 


6 


21 


9i 


II 


5 


8 


18 


8 


\o\ 


4f 


10 


16^ 


7i 


10 


4i 



In this case the rated power of the boiler would be obtained 
by dividing the weight of steam made per hour by the proper 
figure from the above table. 

Assuming the actual kinetic energy of the issuing steam to 
measure the actual available power of the boiler, we find that 
if the size of the orifice is just sufficient to discharge the steam 
as rapidly as it is generated, the work done by the boiler will 
be 



U 



wv 



and the power 



H. P. = 't 550, or H. P. — , 



(I) 



(2) 



when w is the weight of steam made, and v its velocity of out- 
flow per second, the one expression being in British, the ot'her 
in metric measures. 

Again taking Zeuner's figures, we have 



Pressure Velocities per Second. 

Atmospheres. Metres. Feet. 

3 185 607 

4 208 681 

5 227 734 

6 230 775 

8 255 835 

10 260 879 



296 THE STEAM-BOILER. 

and the horse-power actually delivered on this basis would be 
obtained by inverting these values in the expression above. 
So using them, we obtain for the power of the boiler, 



Pressure j^ p '^'^' 



550 



Atmosphkkes. 2^ -ZgUl 

3 1 122(7 in lbs. 5 1 ww in kilos. 

4 l^OW 64TC';« 

5 •• 165TO iyi.i}}Jt 

6 1847*7 847C'/« 

8 io\%v <:)T.w,n 

10 ■ 2377.7 IOS7t7;« 



The work done by the boiler is thus obtained by multiply- 
ing the weight of steam made per second by the figures here 
given. 

This system may be called the natural system of rating 
power. Where a similar system is adopted, but the total re- 
sistance of the atmosphere is allowed for, as proposed by 
Nystrom for the ^' legal " horse-power, the quantity of heat and 
of steam demanded is increased, at usual pressures, about one 
half. Nystrom proposed to assume a fixed rate of combustion 
and proportions of parts. His method maybe illustrated as 
follows : 

A cubic foot of water, when evaporated, forms a definite 
volume of steam ; and if we take the product of the volume of 
water evaporated per hour, the increase of volume by its con- 
version into steam, the pressure of the steam, and divide this 
product by 1,980,000, the quotient, which is the power this 
steam can develop in a non-condensing engine, without expan- 
sion, is the horse-power of the boiler. Suppose, for example, 
that a boiler evaporates 25 cubic feet of water per hour, and 
that the pressure of the steam above the atmosphere is 130 lbs. 
per square inch, or 18,720 lbs. per square foot. The relative 
volume of steam of this pressure is 192.83, so that the increase 
of volume for each cubic foot of water, on its conversion into 
steam, is 191.83 cubic feet, and the horse-power of the boiler is 
the product of 25,191.83, and 18,720 divided by 1,980,000, or 
45-3 +. 



STEAM AND ITS PROPERTIES. 

He would take the power of a boiler to be 



297 



H.P.=^ 



FS\^p 



10 



(2) 



in which formula F and 5 are the areas of grate and heating 
surface in square feet. Thus a boiler having 100 square feet 
of grate and 3000 feet of heating surface, at 75 pounds pressure 
above vacuum, would rate at 



H-P-=-\/- 



00 X 3000 X ^^^75 _ 



10 



510; 



which is far above the usual power of steam-boilers with natural 
draught. 

Small engines, according to Buel, demand steam, ordinarily, 
as below : 



FEED-WATER REQUIRED BY SMALL ENGINES. 



Pounds of Water per 
Pressure of Steam in effective Horse- 

Boiler, by Gauge. power per Hour. 

10 118 



15 
20 

25 
30 
40 
50 



III 
105 
100 

93 
84 
79 



Pressure of Steam in 

Boiler, by Gauge. 

60 


Pounds of Water per 
effective Horse- 
power per Hour. 

75 


70 


71 


80 


68 


90 


65 


TOO 


63 


120 


61 


150 


58 



Pressures lower than 60 pounds are not usually adopted for 
small engines. Good examples of such engines have been 
found by the Author to demand from 25 to 33 per cent less 
steam, or feed-water, than is above given. 

The following are considered by the Author as fair estimates 
of water and steam consumption for the best classes of engines 
in common use, when of moderate size and in good order: 



298 



THE STEAM-BOILER. 

WEIGHTS OF FEED-WATER AND OF STEAM. 

NON-CONDENSING ENGINES. 



Steam Pressure, 


Pounds per H. 


P. PER Hour.— Ratio of Expansion. 


Atmospheres. 


Lbs. per 
sq. in. 


2 


3 


4 


5 


7 


10 


3 


45 


40 


39 


40 


40 


42 


45 


4 


60 


35 


34 


36 


36 


38 


40 


5 


75 


30 


28 


27 


26 


30 


32 


6 


90 


28 


27 


26 


25 


27 


29 


7 


105 


26 


25 


24 


23 


25 


27 


8 


120 


25 


24 


23 


22 


22 


21 


10 


150 


24 


23 


22 


21 


20 


20 



CONDENSING ENGINES. 



2 


30 


30 


28 


28 


30 


35 


40 


3 


45 


28 


27 


27 


26 


28 


32 


4 


60 


27 


26 


25 


24 


25 


27 


5 


75 


26 


25 


25 


23 


22 


24 


6 


90 


26 


24 


24 


22 


21 


20 


8 


120 


25 


23 


23 


22 


21 


20 


10 


150 


25 


23 


22 


21 


20 


19 



It is considered usually advisable to assume a set of practi- 
cally attainable conditions in average good practice, and to take 
the power so obtainable as the measure of the power of the 
boiler in commercial and engineering transactions. The unit 
generally assumed has been usually the w^eight of steam de- 
manded per horse-power per hour by a fairly good steam-en- 
gine. This magnitude has been gradually decreasing from the 
earliest period of the history of the steam-engine. In the time 
of Watt, one cubic foot of water per hour was thought fair; at 
the middle of the present century, ten pounds of coal was a 
usual figure, and five pounds, commonly equivalent to about 
forty pounds of feed-water evaporated, was allowed the best 
engines. After the introduction of the modern forms of en- 
gine this last figure was reduced twenty-five per cent, and the 
most recent improvements have still further lessened the con- 
sumption of fuel and of steam. By general consent, the unit 
has now become thirty pounds of dry steam per horse-power 
per hour, which represents the performance of good non-con- 
densing mill-engines. Large engines, with condensers and 



STEAM AND ITS PROPERTIES. 299 

compounded cylinders, will do still better. A committee of 
the American Society of Mechanical Engineers'^ recommended 
thirty pounds as the unit of boiler-power, and this is now gene- 
rally accepted. They advised that the commercial horse-power 
be taken as ajt evaporation of y:) pounds of water per hour from 
a feed-water temperature of 100° FaJir. into steam at 70 pounds 
gauge pressure, which may be considered to be equal to 34I- 
units of evaporation, that is, to 34^ pounds of water evapo- 
rated from a feed-water temperature of 212° Fahr. into steam 
at the same temperature. This standard is equal to 33,305 
British thermal units per hour.f 

It was the opinion of this committee that a boiler rated at 
any stated power should be capable of developing that 
power with easy firing, moderate draught, and ordinary fuel, 
while exhibiting good economy, and at least one third more 
than its rated power to meet emergencies. 

Any increase of temperature derived from a heater should 
not be credited to the efBciency of the boiler except by agree- 
ment ; and in the latter case tests should be made only with 
feed-water of the temperature observed during the regular 
operation of the boiler. 

* Trans., vol. vi. , Nov. 1881. 

f According to the tables in Porter's Treatise on the Richards Steam-engine 
Indicator, which tables the committee adopt, an evaporation of 30 pounds of water 
from 100° F., into steam at 70 pounds pressure, is equal to an evaporation of 
34.488 pounds from and at 212° ; and an evaporation of 34-^ pounds from and at 
212° F. is equal to 30.010 pounds from 100° F., into steam at 70 pounds pressure. 

The " unit of evaporation" being equal to 965.7 thermal units, the commercial 
horse-power = 34.488 X 965.7 = 33.305 thermal units. 



CHAPTER VII. 

THE DESIGN OF THE STEAM-BOILER. 

146. The Design of the Steam-Boiler is a problem in 
construction which involves vastly more than the mere applica- 
tion of chemical and physical principles, and the calculation of 
areas of grate and heating surfaces. The first step in its solu- 
tion is the study of the conditions under which the steam is to 
be produced and utilized ; the location and space available ; the 
kind and cost of fuel ; the nature and availability of the supply 
of feed-water ; the pressure to be adopted ; the facilities to be 
obtained for repairs ; and many other conditions, of which the 
financial and commercial are as important as any others, must 
all be taken into careful consideration. 

The problem, stated in the most general and comprehensive 
way, may be said to be the following : 

Required : To determine what type, proportions, size, and 
construction of boiler may be made, in the location chosen, and 
under all the natural and artificial conditions found there to 
exist, to supply a given amount of steam at least total risk and 
cost. 

The business aspects of the case must be as conscien- 
tiously studied by the designing engineer as those of pure en- 
gineering. 

The design of the steam-boiler is thus a problem in en- 
gineering which demands careful consideration, accurate knowl- 
edge of the principles controlling proportions and performance, 
and perfect familiarity with the conditions to be met in the 
case in hand. 

147. The Choice of Type of Boiler and its Location is 
the first step to be taken preparatory to commencing the de- 
sign. The type best adapted for the special case is determined 
by the conditions of location and purpose, as whether station- 



THE DESIGN OF THE STEAM-BOILER. 3OI 

ary, portable, locomotive, or marine ; by the pressure and quan- 
tity of steam demanded ; by the character of the feed-water 
and fuel, and the cost of obtaining it ; by the facilities to be 
had* for repairs, etc. 

Where the boiler is' to be used on land, the standard loco- 
motive and stationary boilers may be used, if found otherwise 
advisable ; but on shipboard it is essential that the boiler should 
be '' self-contained," and the common stationary boilers cannot 
be employed. Each application is best made, as a rule, by 
the employment of some one of those forms which have been 
classed above, and certain types are thus standard for each 
location. 

Among stationary boilers the plain cylindrical is chosen 
when the cost of fuel is low, when the feed-water is bad, or 
w^hen the facilities for repairing are not good. As the necessity 
for economy in fuel-consumption becomes greater, and when 
the character of the feed-water is good, the more complicated 
flue or tubular boilers are selected ; or the dictates of prudence 
may lead to the selection of some one of the so-called " safety" 
or '' sectional " boilers, even where cost and other considera- 
tions would weigh against them. 

The most common form of stationary boiler in the United 
States, in ordinary good locations, is the cylindrical tubular 
boiler ; in Great Britain the Cornish and the Galloway boilers 
are much used ; while on the continent of Europe the '' ele- 
phant" boiler is more common. In all directions, however, the 
safer forms of boiler are gaining ground. 

The " portable " boiler is usually an upright tubular, with 
firebox beneath, for very small powers, and a horizontal boiler 
of the locomotive type for larger sizes. It must always be " self- 
contained " in the sense of having no " setting," and is com- 
monly made the foundation or bed for its attached engine, 
somewhat as in locomotives. 

The locomotive boiler has become fixed in type, and nearly 
fixed in proportions. All builders adopt the horizontal, cylin- 
drical tubular shell with firebox. Here, as in all cases in which 
high pressures are employed, cylindrical or strongly stayed sur- 
faces are found essential to safety and durability. Many other 



302 THE STEAM-BOILER. 

designs of boiler have been proposed and experimentally em- 
ployed for locomotives, but none has survived. 

The marine steam-boiler is the product of a long process of 
evolution which has led to the gradual reduction of a variety 
of forms to a few standards. Thus, at sea, the ''drum" or 
Scotch boiler, described in article 19, has become almost uni- 
versally adopted where high pressures are employed, as it is 
stronger, more compact, and more economical than its rivals, 
and is self-contained. 

The location of a boiler is sometimes a matter of choice 
with the engineer preparing the plans, and may be one of 
serious importance. Where possible it should always be so 
chosen that the boiler may be easy of access for inspection and 
repair ; it should be free from special danger to lives or sur- 
rounding property in case of accident, and the site selected 
should be dry and well protected against the weather. The 
nearer the engine or other point at which its steam is delivered 
the better. Only sectional boilers should be placed under 
buildings. Shell-boilers should have boiler-houses constructed 
for them apart from the larger and more important structures 
to which they are auxiliary, and this precaution is especially' 
advisable for cases, as mills, in which many lives may be en- 
dangered. The risk involved is not great where these boilers 
are well designed and constructed ; but the prudent engineer 
avoids even moderate risk where a life is involved. 

When the space is restricted in floor-area, but of good 
height, the upright tubular boiler is selected ; if the floor-area 
is unrestricted, but head-room is small, the horizontal forms of 
boiler are chosen. Good forms of " safety " boilers may be 
placed wherever they can be given room, provided they are 
accessible for inspection, cleaning, and repairs. 

148. The Choice of Fuel and of Method of Combustion 
is commonly necessarily made before the design can be pro- 
ceeded with. The fuel is, as a rule, selected mainly with a view 
to commercial efficiency ; but the presence of any observable 
quantity of sulphur in coal justifies its rejection at even con- 
siderable pecuniary sacrifice. That fuel is best which produces 
the required quantity of steam with certainty and regularity 



\ 



THE DESIGN OF THE STEAM-BOILER. 303 

under the given conditions, and at minimum total cost for 
purchase, transportation and handUng, storage, interest and 
insurance, and wear and tear of apparatus. As a rule, the least 
costly fuels are most economical, if the furnace is properly 
adapted to them ; but it is not always so, and the user will 
generally solve the problem by experiment and experience. 
The conditions of the market are very apt to control, and 
anthracite fuel in the Eastern United States, bituminous coals 
throughout the West, and wood in forested countries are 
naturally the staple fuels. On the border lines, or even within 
either territory, prices may be so adjusted that the question 
may be difficult to decide until after prolonged trial of two or 
more kinds which may be available. In the case of the "soft" 
coals the decision of the question whether the fuel shall be 
used in its natural state, or coked, may often demand con- 
sideration. For metallurgical purposes coke is commonly 
used, but for steam-boilers the raw coal is most generally 
adopted. 

The combustion may be produced by either a natural 
chimney draught or a forced draught, created by a fan, a steam- 
jet, or other artificial means. With very fine coal, or where the 
grate-area or the boiler itself is so small as to make the rate 
of combustion due to natural draught insufficient, the blast is 
employed. The locomotive and the torpedo-boat illustrate 
this case. A closed fire-room, made air-tight, and into which 
the blast is driven and allowed to enter the furnace precisely 
as with a chimney draught, is regarded by many engineers as 
the best method of securing rapid combustion. Where the 
area of heating-surface is the same in proportion to the amount 
of coal burned, this system is fully as economical as the others. 
The proportion of heating to grate surface being fixed, or 
nearly constant, as is common, the slower combustion, down to 
certain limits is naturally the more efficient. Natural draught 
is to be preferred where the desired amount of steam may be 
made by that system. 

149. The Conditions of Efficiency in steam-boilers are 
those affecting the production, the transfer, and the storage of 
the heat-energy derivable from the fuel. These have already 



304 THE STEAM-BOILER. 

been considered. En resum^ : the efficient production of heat 
requires the concentrated combustion of the fuel, with the 
minimum air-supply consistent with the complete combination 
of its oxidizable elements with oxygen, and the attainment of 
maximum temperature. The efficient transfer and storage in 
the steam of this heat demands that it be liberated at maxi- 
mum temperature, that the heating-surfaces be of great extent 
in proportion to the weight of fuel burned and to the quantity 
of heat liberated, and that these surfaces be effective in absorp- 
tion of heat. The formula deduced in Chapter IV. for effi- 
ciency of heating-surface gives a measure of the efficiency of 
the boiler when the value of the fuel is know^n, and includes 
efficiency of transfer and of storage. 

150. The Principles of Design, in the case of the steam- 
boiler, involve those of strength of materials and of structures, 
the determination of the size, form, and proportions of parts ; 
the relation of area of heating and of grate surface to fuel 
burned ; the character and proportions of accessory parts ; in 
fact, the application of all the data and the laws which have 
been studied in the preceding portions of this work. The de- 
signing engineer must determine the form and proportions of 
a vessel in which is to be generated a given quantity of steam 
with satisfactory efficiency and safety, and with as nearly per- 
manent commercial success as possible. 

The settlement of the general proportions of the structure 
is made with reference to the above considerations ; but gen- 
eral experience has brought these proportions into a fairly 
definite relation, and, as an illustration, the better classes of 
boiler rarely have a less ratio of heating to grate surface, where 
natural draught is adopted, than about 25 to i, or a higher 
ratio than 40 to i. With more intense combustion and forced 
draught this proportion is considerably increased. The best 
proportion is probably usually capable of fairly exact calcula- 
tion by a method to be considered at some length in a later 
chapter. Boiler-power is very often calculated, in cases of 
ordinary practice, by allowing a certain number of square feet 
of heating-surface to the horse-power. Thus, the following 
may be taken as a fair average set of figures : 



THE DESIGN OF THE STEAM-BOILER. 305 

Plain cylinder-boiler 8 

Flue-boiler 10 

Water-tube or sectional boiler 12 

Locomotive boiler 13 

Return tubular boiler 15 

Upright tubular boiler 18 

Careful calculation should be resorted to in every impor- 
tant case. 

In designing boilers the effort of the engineer should be — - 
(i) To secure complete combustion of the fuel without 
permitting dilution of the products of combustion by excess 
of air. A combustion-chamber is usually desirable. 

(2) To secure as high temperature of furnace as possible. 

(3) To so arrange heating-surfaces that, without checking 
draught, the available heat shall be most completely taken up 
and utilized and the most complete and rapid circulation se- 
cured, both for the water and for the furnace-gases. 

(4) To make the form of boiler so simple that it may be 
constructed without mechanical difficulty or excessive expense, 
and to arrange for ample water-surface, as well as large 
steam and water capacity, so as to insure against serious fluc- 
tuation of steam-supply. 

(5) To give it such form that it shall be durable, under the 
action of hot gases, and of corroding elements of the atmos- 
phere. 

(6) To make every part accessible for cleaning and repairs. 

(7) To make all parts as nearly as possible uniform in 
strength, and in liability to loss of strength with age, so that 
the boiler, when old, shall not be rendered useless or dangerous 
by local defects. 

(8) To adopt a reasonably high •' factor of safety" in pro- 
portioning parts, and to provide against irregular strains of all 
kinds. 

(9) To provide efficient safety-valves, steam-gauges, mud- 
drums, and other appurtenances. 

(10) To secure intelligent and very careful management. 

In securing complete combustion — the first of these desiderata 
— an ample supply of air and its thorough intermixture with the 



306 THE STEAM-BOILER. 

combustible elements of the fuel is essential ; for the second — 
high temperature of furnace — it is necessary that the air-supply 
shall not be in excess of that absolutely needed to give com- 
plete combustion. The efficiency of a furnace is measured by 

T — T 
E — - — 

in which E represents the ratio of heat utilized to the whole 
calorific value of the fuel ; T is the furnace temperature ; 2"' 
the temperature of the chimney, and t that of the external air. 
Hence the higher the furnace-temperature and the lower that 
of chimney, the greater the proportion of available heat. 

It is further evident that, however perfect the combustion, 
no heat can be utilized if either the temperature of chimney 
approximates to that of the furnace, or if the temperature of 
the furnace is reduced by dilution to that of the chimney. 
Concentration of heat in the furnace is secured, in some cases, 
by special expedients, as by heating the entering air, or, as in 
the Siemens gas-furnace, heating both the combustible gases 
and the supporter of combustion. Detached fire-brick fur- 
naces have an advantage over the '' fireboxes" of steam-boilers 
in their higher temperature ; surrounding the fire with non- 
conducting and highly heated surfaces is an effective method 
of securing high furnace-temperature. 

In arranging Jicating-stirface^ the effort should be to impede 
the draught as little as possible, and so to place them that the 
circulation of water within the boiler should be free and rapid 
at every part reached by the hot gases. 

The direction of circulation of water on the one side and of 
gas on the other side the sheet should, whenever possible, be 
opposite. The cold water should enter where the cooled gases 
leave, and the steam should be taken off farthest from that 
point. The temperature of chimney-gases has thus been re- 
duced by actual experiment to less than 300° Fahr., and an 
efficiency equal to 0.75 to 0.80 the theoretical is attainable. 

The extent of heating-surface simply, in all of the best 
forms of boiler, determines the efficiency, and the disposition 



THE DESIGN OF THE STEAM-BOILER. 307 

of that surface seldom affects it to any great extent. The 
area of heating-surface may also be varied within very wide 
limits without greatly modifying efficiency. A ratio of 25 to i 
in flue and 30 to i in tubular boilers represents the relative area 
of heating and grate surfaces in the practice of many of the 
best-known builders. 

TJie factor of safety is usually too low. The boiler should 
be built strong enough to bear a pressure at least six times the 
proposed working-pressure. As it grows weak with age, it 
should be occasionally tested to a pressure at least double the 
working-pressure, which latter should be reduced gradually to 
keep within the bounds of safety. 

151. The Controlling Ideas in designing dictate the follow- 
ing procedure. The engineer determines — 

(i) The height of chimney, and rate of combustion desira- 
ble or practicable. 

(2) The type of boiler, having regard to the character of 
Avater to be used as " feed," and the costs of construction, opera- 
tion, and maintenance. 

(3) The quantity of steam that will be demanded. 

(4) The efficiency of boiler that it will be economical to se- 
cure, according to the principles to be given, and thus the ratio 
of heating to grate surfaces. 

(5) The kind and the quantity of fuel required, Avith the 
given or proposed efficiency, to produce the demanded quan- 
tity of steam. 

(6) The total areas of grate and of heating surface required 
to burn that fuel and to make that steam. 

(7) The forms, sizes, and proportions of details. 

The dimensions and proportions of the boiler plant being 
thus determined, the engineer decides what amount of power 
shall be obtained from a single boiler, and thus how many boil- 
ers are to be constructed, the area of heating and grate surface 
to be given each ; and he finally decides upon the form of set- 
ting, and method of making steam and water connections. 

It then remains only to make a drawing of the boiler, 
which shall show its form and dimensions, the arrangement of 



308 THE STEAM-BOILER. 

stays, pipes, safety, and other attachments, and the setting. 
The first plan constructed will usually require some modifica- 
tion to adapt it exactly and satisfactorily to the wants of the 
user; which changes being made, the boiler may be constructed 
from the drawing. The thickness of shell, size of tubes or flues, 
sizes, methods, and distribution of stays, and similar matters of 
detail, are settled by well-known rules of practice, or by the 
consideration of the peculiar conditions met with in the case in 
hand. 

Especial care should be taken to give all parts ample strength, 
with a fair and safe allowance for corrosion ; to see that every 
part is easily accessible for inspection and repair; that all de- 
tails are of good form and proportions ; and that all accessories 
and attachments are the best and safest of their kind. 

The Steam-pressure to be adopted will necessarily be one of 
the first matters to be considered and settled ; both because it 
has an important bearing upon the efficiency of the engine and 
because it must be kept in view in the selection of the type 
and size of boiler. The tendency is constantly in the direction 
of higher steam-pressure, and the consequent adoption of the 
simpler, stronger, and safer kinds of boiler. This directly con- 
flicts with the commercial considerations affecting boiler-con- 
struction, especially of the common forms of shell-boiler. The 
larger the boiler, as a rule, the cheaper, comparatively, its con- 
struction, the less the cost of setting and of installation, and 
the higher its economy in operation. A large shell, however, 
must be made of thicker iron, and is always somewhat less ab- 
solutely safe than a similar smaller structure. 

A limit is thus being continually approached because of the 
fact that the net gain is less and less as the increase occurs at 
higher pressures. An increase from lOO to 200 pounds may 
give a calculated gain of 12 or 15 percent; but the net gain 
will be actually much less, and may not be enough to compen- 
sate the increased costs and risks. At the present day, pres- 
sures of 125 to 1 50 pounds are not unusual; but many engineers 
consider it inadvisable to go much farther in the direction 
of increasing pressure, and the tendency of modern practice is 



THE DESIGN OF THE STEAM-BOILER. 



309 



to restrict the adoption of such higher pressures to the cases in 
which the sectional types of boiler are used. 

As illustrating the general effect of increasing pressures, and 
the progressive diminution of the rate of gain, Mr. H. F. 
Smith has given the following tables of weight of steam and 
coal demanded per hour and per horse-power, by a perfect 
steam-engine, calculated on the assumption that 1 100 thermal 
units per pound of coal are utilized by the boiler, which corre- 
sponds to an evaporation of about iiy^ parts by weight of 
water from and at the boiling-point, per one part of coal — a re- 
sult attainable with good coal : 

STEAM AND FUEL CONSUMPTION IN A PERFECT STEAM-ENGINE. 



Boiler 
Pressure. 


Tempe 


RATURE. 


Steam. 
Per I. H. P. per hour. 


Perl. 


Coal. 
H. P. per hour. 


Per Gauge. 




Non-con- 
densing. 


Con- 
densing. 


Non-con- 
densing, c 


Con- 
iensing. 


Lbs. Atinos. 


Fahr. 


Cent. 


Lbs. Kil. 


Lbs. Kil. 


Lbs. Kil. L 


bs. Kil. 


300 20 


421.7 


216.5 


10.48 4.8 


6.16 2.7 


0.98 


44 


64 .29 


250 i6§ 


405-9 


207.7 


II. 19 5.1 


6 


39 2.9 


1.04 


45 


66 


30 


200 i3§ 


387.6 


197 


5 


12.16 5.5 


6 


68 3.0 


1. 13 


51 


69 


31 


175 "§ 


377.1 


191 


7 


12.81 5.7 


6 


87 3 I 


1. 18 


54 


71 


32 


150 10 


365.6 


185 


3 


13.63 6.2 


7 


09 3-2 


1.25 


57 


73 


33 


125 81 


352 6 


167 





14.71 6.7 


7 


37 3-8 


1-35 


60 


75 


34 


100 6§ 


337.6 


159 


8 


16.24 7.4 


7 


71 3-5 


1.48 


67 


78 


35 


90 6 


330.9 


166 


I 


17.05 7.7 


7 


89 3.6 


1.55 


70 


80 


36 


80 5§ 


323.6 


162 





18.03 8.2 


8 


09 3-7 


1.64 


75 


82 


37 


75 5 


319.8 


159 


9 


18.60 8.5 


8 


19 3.7 


1.69 


77 


83 


38 


70 4l 


315.7 


157 


6 


19-25 8.7 


8 


32 3-8 


1-75 


80 


84 


39 


60 4 


307.1 


152 


8 


20.83 9.5 


8 


59 3.9 


1.88 


85 


87 


39 


50 35 


297.5 


147 


5 


22.95 10.4 


8 


92 41 


2.07 


90 


90 


40 


45 3 


292.2 


144 


5 


24.53 11. I 


9 


ir 4 I 


2.19 I 


00 


91 


40 



The table shows that at high pressures the gain of economy is 
very slow, and that the very best modern engines waste a large 
part of the steam passing through the cylinder. At 125 pounds, 
if there were no losses, three fourths oi a pound of coal per hour 
would furnish one indicated horse-power , but very few engine- 
builders can be found who are willing to guarantee an indicated 



3IO 



THE STEAM-BOILER. 



horse-power with less than one a7id three fourths of a pound of 
coal per hour under the best of conditions. 

A pound of coal, if all the heat were utilized, would evapo- 
rate 15 pounds of water from and at the boiling-point. Many 
boilers actually evaporate \\\ pounds of water with an effi- 
ciency of 75 per cent. 

An engine w^orking perfectly would develop one indicated 
horse-power with /f pounds of steam (of 125 pounds initial 
pressure) per hour ; the best actual engines consume more than 
double this quantity. 

Mr. G. H. Barrus gives the following as the probable actual 
steam-consumption of good engines:"^ 

FEED-WATER CONSUMPTION FOR NON-CONDENSING ENGINES. 



Initial 




Feed-water 


Initial 




Feed-water 


pressure 


Mean effective 


consumed per 


pressure 


Mean effective 


consumed per 


above 


pressure. 


I. H. P. 


above 


pressure. 


I. H. P. 


atmosphere. 


"^ Lbs. 


per hour. 


atmosphere. 


Lbs. 


per hour. 


Lbs. 




Lbs. 


Lbs. 




Lbs. 


At 


10 Per Cent Cut-off. 


At 


30 Per Cent Cut-off. 


40 


1.32 


153-24 


40 


16.95 


33-52 


50 


5 .01 


52.52 


50 


23-71 


29-35 


60 


8.70 


37.26 


60 


30.47 


27.24 


70 


12.39 


30-99 


70 


37 21 


25.76 


80 


16.07 


27.61 


80 


43-97 


24.71 


90 


19.76 


25-43 


90 


50.73 


23.91 


100 


23-45 


23.90 


100 


57-49 


23.27 


At 


20 Per Cent Cut-off. 


At . 


p Per Cent Cut-off. 


40 


10.22 


38.13 


40 


22.24 


32-79 


50 


15-67 


30.98 


50 


29.99 


29.72 


60 


21.12 


27-55 


60 


^7-75 


27.92 


70 


26.57 


25-44 


70 


45-50 


26.26 


80 


32.02 


24.04 


80 


53-25 


25.76 


90 


37-47 


23.00 


90 


61. ot 


25.03 


100 


42.92 


22.25 


100 


68.76 


24.47 



At 50 Per Cent Cut-off. 



40 


26.40 


33.16 


80 


60.44 


26.99 


50 


34.91 


30.53 


90 


68.96 


26.32 


60 


43.42 


28.94 


100 


77.48 


25.78 


70 


51-94 


27.79 









■* The Tabor Indicator. 



THE DESIGN OF THE STEAM-BOILER. 



311 



FEED-WATER CONSUMPTION FOR CONDENSING ENGINES. 



Initial 




Feed-water 


Initial 




Feed-water 


•pressure 


Mean efifective 


consumed per 


pressure 


Mean effective 


consumec per 


above 


pressure. 


I. H. P. 


above 


pressure. 


I. H. P. 


atmosphere. 


Lbs. 


per hour. 


atmosphere. 


Lbs. 


per hour. 


Lbs. 




Lbs. 


Lbs. 




Lbs. 


At 


5 Per Cent Cut-off. 


At 20 Per Cent Cut-ofe. 


40 


9-34 


18.99 


40 


23 83 


19.00 


50 


11.88 


18.51 


50 


29 


28 


18 


74 


60 


14.42 


18 22 


60 


34 


73 


18 


98 


70 


10.90 


17.96 


70 


40 


18 


18 


40 . 


80 


19-50 


17.76 


80 


45 


63 


18 


27 


90 


22.04 


17-57 


90 


51 


08 


18 


14 


100 


24.58 


17.41 


100 


56-53 


18.02 


At 


[o Per Cent Cut-off. 


At 30 Per Cent Cut-off. 


40 


14.96 


18.25 


40 


30-54 


20.57 


50 


18.65 


17.91 


50 


37 


30 


20.35 


60 


22.34 


17.68 


60 


44 


06 


20. 19 


70 


26.03 


17-47 


70 


50 


81 


20.04 


80 


29 72 


17-30 


80 


V 


57 


19.91 


90 


33 41 


17-15 


90 


64 


32 


1Q.78 


ICO 


37- 10 


17.02 


100 


71.08 


19.67 


At 


15 Per Cent Cut-off. 


At 40 Per Cent Cut-off. 


40 


19.72 


,8.41 


40 


35-84 


21.94 


50 


24.36 


18.11 


50 


43 


59 


21.76 


60 


29.00 


17-93 


60 


51 


35 


21.63 


70 


33-65 


17-75 


70 


59 


10 


21.49 


80 


38.28 


17.60 


80 


06 


85 


21.36 


90 


42.92 


17-45 


90 


74 


60 


21.24 


100 


47-56 


17-32 


100 


82.36 


21.13 



152. Safety and Efficiency vs. Cost may be taken as the 
most serious part of the problem to the designer and user of 
steam-boilers. The safety of the boiler being a first considera- 
tion, it becomes at once a question how far the engineer is justi- 
fied in sacrificing money and special advantages to secure safety, 
and how closely he may be practically able to approximate ab- 
solute security. To increase strength of structure or of parts 
means to enlarge the dimensions, and to thus increase expense ; 
to select a specially safe type, or peculiarly safe construction, 
is usually to meet the same objection ; and it is soon found 
that there is a certain golden mean between maximum safety 
and impracticable expense which gives most satisfactory re- 
sults. For ordinary cases, this is probably found not far from 
those proportions which give a " factor of safety" of about six 
for the important parts of the boiler, although good authori- 



312 THE STEAM-BOILER. 

ties advise eight, and even ten, and general practice often falls 
to less than four. 

The same difficulty arises when it is attempted to attain 
high efficiency. This must be done by extension of heating- 
surface and correspondingly increased first cost ; and it is 
readily shown, as in Chapter XIII., that business considera- 
tions fix the limit of efficiency to be sought. This efficiency 
being given, the size and proportions of boiler become at once 
determinable. Thus accepting Rankine's formula for effici- 
ency, already given in article 98, and taking the desired 
efficiency as given by calculation as E^ the ratio of heating-sur- 

E 
face divided by fuel burned, -— := R, will be obtained thus : 

^=r+4^T ^'> 

^ = ^j^ (^) 

Taking as common values E = 0.70, A = 0.5, B = i, 

'^=„^:=°''«=p « 

and the ratio of heating to grate-surface would h^ S = — ~] if 

0.86 

F =^ 15, 5= 17.5. Taking a rather high efficiency, E ■— 0.80, 
R= 0.5, and 5= 30. 

153. Water-tubes and Fire-tubes have, respectively, 
their own special advantages and disadvantages, and these 
differ in their importance in different types of boiler. It was 
shown by experiments directed by Engineer-in-chief B. F. 
Isherwood of the U. S. Navy,^ that the water-tube boiler as 
constructed for marine purposes with vertical tubes is some- 
what more economical than the horizontal fire-tube boiler of 
otherwise similar type, and the former excels in the perfection 
of its circulation and the readiness with which it can be freed 
from incrustation ; it, however, makes a heavier boiler, and the 

* Experimental Researches in Steam Engineering. 



THE DESIGN OF THE STEAM-BOILER. 3I3 

water-tube is less easily plugged if leaking. This latter diffi- 
culty, and the inconveniences and dangers arising from the 
a'ccumulation of salt in marine boilers when water from in- 
jured tubes evaporates in the tube-box, have caused the 
disuse of this class of boilers. The " sectional " class of water- 
tube boilers is less subject to such objections. 

Water-tubes are always set either vertical or steeply inclined, 
as horizontal or nearly horizontal water-tubes are liable to 
rapid destruction, and are comparatively inefficient because 
of the defective circulation invariably distinguishing them. 
The fire-tube may be used in any position, but is usually 
placed horizontally. 

The general experience of engineers has been such as to 
lead them to adopt the water-tube in the so-called "safety" 
class of boilers and the fire-tube in others. The water-tube is 
usually placed at an angle, in these boilers, of about thirty de- 
grees with the horizontal. In the " Field tube" the position 
is vertical, or nearly so ; the lower end is closed, and an in- 
ternal "circulating tube" permits the descent of a solid column 
of water while the mingled steam and water currents gene- 
rated by the heat applied to the exterior of the main tube 
rise unobstructed to the surface. 

Messrs. Porter and Allen found that water-tubes, closed at 
the bottom and set at an angle of about thirty degrees with 
the vertical, were capable of doing good work, and had a 
sufficiently good circulation to give extraordinarily high evapo- 
rative power. In all standard forms of " shell-boilers" the 
water-tubes are placed vertically, and are grouped in a low, 
long, and usually narrow tube-box, several of which tube-boxes 
are placed side by side in large boilers. 

The fire-tube stands vertically in the common " upright" 
boiler, and is set horizontally, as has been seen in Chapter I., 
in all the other common forms. 

As constructed by the best-known builders, the water-tube 
is expected to do about twenty per cent more work than the 
iire-tube of equal area. The water-tube shell-boiler is in some 
respects safer than the fire-tube boiler; since the water level 
can be carried below, and often a considerable distance below, 



314 THE STEAM-BOILER. 

the top of the tube without endangering it. Low water with 
the horizontal fire-tube is always dangerous. 

154. Shell and Sectional Boilers, compared in other re- 
spects than in reference to safety, in which attributes the latter 
are specially constructed to excel, are found, when equally 
well designed and constructed, and equally well managed, to 
stand on substantially the same level. 

The two types of boiler in most common use are the water- 
tube sectional and the cylindrical fire-tube (shell) boiler. The 
latter is in the more extensive use, its cost, as a rule, being 
less, its regularity of steam-supply and uniformity of water- 
level greater, while its unity of structure, its convenience of 
access for inspection and repair, and perhaps more than all, 
the fact of its having a longer history, and being the product 
of a kind of survival of the fittest of the older types, giving it 
a hold upon the market that later forms of boiler have not 
secured. The former of these two classes has the grand ad- 
vantage of safety against disruptive disastrous explosions, has 
equally good or better circulation and general efficiency, less 
weight and volume for equal powers, and greater reliability in 
its details of structure. Its joints are an objection, and its 
usually less steady operation is a disadvantage ; but it is 
rapidly coming into favor among engineers, and into use as 
well. 

The Author would often use the shell-boiler where commer- 
cial reasons would dictate such use, and, wherever practicable, 
would select the externally fired cylindrical fire-tube boiler, 
but would never place a shell-boiler under a building in which 
its explosion would endanger life or much property : the 
*' safety" class of boiler would be the only form to be wisely 
adopted in such locations. Shell-boilers should usually be 
placed in detached boiler-houses, and so set, as to position, that 
danger shall be made a minimum, i.e., never pointing toward 
other buildings. 

155. Natural and Forced Draught both have their advan- 
tages and their disadvantages. Chimney draught, unaided, 
gives a good supply of air to the fire, such as answers the pur- 
pose well for all ordinary work ; is free from the objections 



THE DESIGN OF THE STEAM-BOILER. 315 

introduced with all machinery, and especially those arising from 
uncertainty of absolutely reliable continuous operation, and an 
equally certain expense for wear and tear. For the intense 
draught and large air-supply needed when a large amount of 
fuel is to be burned on a small area of grate, the size and 
especially the height of chimney required, and its cost, become 
serious matters, and for such cases a forced draught is the only 
suitable system. 

There are two principal systems of forced draught, as al- 
ready noted: that in which the air is forced directly into the 
ashpits through conduits leading from the fan or other source 
of the blast ; and that in which the current is driven into the 
fire-room, or ''stoke-hole," which is made air-tight for this pur- 
pose, and thence finds its way to the furnaces precisely as when 
a natural draught is adopted. Of these the first is the older 
and more common method ; while the second is coming into 
use, particularly on torpedo-boats and elsewhere where enor- 
mously high rates of combustion are to be attained and kept up. 
By the older system the change from the forced to the natural 
draught is very conveniently made ; but there is more difficulty 
in handling the fires, and the blowing of dust out into the 
room, and the danger of melting down the grate-bars, are two 
decided disadvantages, which are not inherent with the system 
involving the adoption of the air-tight fire-room. In the latter 
case the fires are as conveniently and nearly as comfortably 
managed as with natural draught ; and as all air passes to the 
furnaces through the fire-room, if it is well directed, the ventila- 
tion and cooling of the room and the comfort of the men are 
comparatively well insured. 

A later and in some respects most satisfactory system is 
that in which the air is drawn into the boiler-room by a fan 
placed as near the furnace as possible, cind then forced through 
ducts into the ashpit, and into the interior of hollow furnace- 
doors in such manner as to intercept any gas that would other- 
wise be liable to find its way outward at the furnace mouth. 

The Power required for Forced Draught is easily calculated 
thus: 



3l6 THE STEAM-BOILER. 

Let/ = pressure of blast per square foot ; 
w = weight of fuel burned per minute ; 
Vq = volume of air per pound of fuel, at melting-point 

of ice ; 
T^ = temperature, absolute, at 0° Fahr.; 
T= " " of entering air; 

C = coefificient of efficiency of blast apparatus. 
Then the horse-power demanded will be 

H. P. = /^o^^^ 



33,oooT^C' 

Thus for 100 square feet of grate, at 60 pounds burned per 
hour or one pound per minute, per square foot, 200 cubic feet 
of air at 32° F. per pound of fuel, when T^ =493.2, T= 532.2, 
C = i,p =^ 3 inches of water = 16 pounds per square foot. 

16 X 200X I X 532.2 

H. P. =z — — = 20 nearly. 

33,000 X 493-2 X i 

But good engines with such boilers should develop 2000 
horse-power. The cost of blast would thus be about one per 
cent of the total power ; while with natural draught the cost 
would probably be in vastly greater proportion in the form of 
waste heat. 

An efficient water-circulation is very important, and the 
best boiler, as already stated, the most efficient as well as the 
safest, is that in which, other things being equal, the circulation 
is most complete, general, rapid, and steady. In nearly all 
boilers the circulation is a *' natural " one ; but occasionally, as 
in Pierce's rotary boiler,* as tested by the Author, and later 
at the U. S. Centennial Exhibition of 1876, and in the boiler 
of Professor Trowbridge, the circulation is a '' forced " one. 
The last-named engineer made experiments,! assisted by Messrs. 
T. W. Mather and J. F. Klein, graduate students of the Shef- 

* Reports on Steam-boilers at the U. S. Centennial Exhibition, 1876. 
f Heat and Steam-engines, p. 146. 



THE DESIGN OF THE STEAM-BOILER. 317 

field Scientific School, to determine the efficiency of forced 
circulation. The difficulty of constructing very small steam- 
generators having sufficient strength to resist great pressure, 
and at the same time a high rate of evaporation with reason- 
able economy, has long been recognized. On account of this 
difficulty the use of very small engines is limited. The boiler 
in such engines must have such large proportions relatively to 
the engine that it ceases to be an economical apparatus. 

The object of these experiments was to reduce the heating- 
surface, and at the same time make it more efficient by a 
forced and continuous circulation of the water in the boiler, 
through the means of a circulating pump. Various combina- 
tions and modes of circulation were tried, with results which 
appear conclusive. A steam-generator of very small volume 
and weight, made of coils of gas-pipe, and consequently having 
a resistance of several thousand pounds per square inch, was 
made to evaporate quantities of steam per hour which by ordi- 
nary processes would require a boiler of very much greater 
volume. The principle of forced circulation has not often been 
employed for this purpose, but there is reason to believe that it 
may become practically useful. 

156. Special Conditions affecting Design thus arise in 
many cases, and may absolutely dictate the form of the boiler 
chosen and the place and method of its location and setting. 
Financial considerations often control ; the matter of safety 
should always be kept in view, and may often be the deciding 
element in the problem. Peculiarities of location may, and 
often do, determine the size and form of the boiler to be 
chosen, and even the character of the feed-water will frequently 
decide such choice. No design is satisfactory except it meets 
in the most satisfactory manner pucticable every element going 
to make up the whole problem, and is at the same time suitable 
for the location, the specific work to be done, and properly 
meets the pecuniary interests of those concerned, as well as 
gives the safest and most efficient arrangement possible under 
the circumstances. 

157. The Chimney Draught, and the size, height, and 
general construction of chimney and flues, are among the first 



3l8 THE STEAM-BOILER. 

of the details to be settled when preparing to design a steam- 
boiler. 

The chimney draught is the first condition to be studied, 
since upon it primarily depends the power and performance 
of the boiler. The intensity of the draught in a well-propor- 
tioned chimney will vary nearly as the square root of its height. 
The quantity of fuel burned on the unit-area of grate is thus 
determined, assuming the chimney section properly propor- 
tioned to the work. The sectional area of the chimney-flue 
should be carefully proportioned to the maximum weight of 
fuel to be burned in the unit of time. 

Chimneys are required to carry off obnoxious gases, and to 
produce a draught. Each pound of coal burned commonly 
yields from 15 to 50 pounds of gas, the volume of which varies 
directly as the absolute temperature. 

The weight of gas carried off by a chimney in a given time 
depends upon size of chimney, velocity of flow, and density of 
gas. But as the density decreases directly as the absolute 
temperature, while the velocity increases, with a given height, 
nearly as the square root of the temperature, there is a tem- 
perature at which the weight of gas delivered is a maximum. 
This is about twice the absolute temperature, or 550° above, 
the surrounding air. At 550° the quantity is only four per 
cent greater than at 300° above the ordinary temperature. 
Height and area are practically the only elements necessary 
to consider in an ordinary chimney. 

The intensity of draught is independent of size, and varies 
directly with the product of the height into the difference of 
temperature. 

The intensity of draught needed varies with the kind of 
fuel and the rate of combustion desired, being least for wood 
and other free-burning fuels, and greatest for the finer coals 
and *' slack" or "brees," the latter requiring a chimney one 
hundred and fifty to two hundred feet high, and a difference of 
pressure measured by an inch or more of water. 

The volume and weight of gas discharged from any furnace 
may be calculated as if it were of the density of air at the same 
temperature, the volume being \2\ cubic feet per pound, nearly, 



THE DESIGN OF THE STEAM-BOILER 



319 



or about three fourths of a kilogram to the cubic metre. 
Adopting British measures, if Fbe the volume per pound at 
/", absolute, Fahrenheit degrees, 



V: 



*^ O 'X' ' 



(I) 



and we obtain, allowing, respectively, 12, 18, or 24 pounds to 
be equal to 150, 225, and 300 cubic feet, the following volumes 
of gases as originally calculated by Rankine : 

VOLUMES OF GAS PER POUND OF FUEL IN CUBIC 
FEET. (RANKINE.) 



T. 


Air-Supply in Pounds per Pound of Fuel. 


12 


18 


24 


4640° 

3275° 
2500° 
1832° 
1472° 
1112° 
752° 
572° 

392^ 
212° 
104° 

68° 
32° 


155I 
II36 
906 
697 
588 
479 
369 
314 
259 
205 
172 
161 
150 


1704 

1359 
1046 
882 
718 
553 
471 
389 
307 
258 
241 
225 


1812 

. 1395 
1176 

957 
73S 
628 

519 
409 

344 
322 
300 



If w denotes the weight of fuel burned in a given furnace 
per second ; 

Fq, the volume at 32° of the air supplied per pound of fuel ; 

T^. the absolute temperature of the gas discharged by the 
chimney ; 

A, the sectional area of the chimney; then the velocity of 
the current in the chimney in feet per second is 



At. ' 



(2) 



and the density of that current, in pounds to the cubic foot, is 
very nearly as in (3). 



320 THE STEAM-BOILER. 

Since one cubic foot of air at the temperature T^ weighs 
about 0.0807 pound, and the weight, on the assumption of 
uniform mean density of air and gases, is, at Z^, 0.0807 F^+i, 
and its mean density is 

0.0807 F,+ I . ^ ^ 
D^ = y , and at T, 

^ o 

D=^{o.oSo7 + y) (3) 

Multiplying D by the height of chimney, H, the weight of 
the column per unit section of its area, or, as here taken, in 
pounds on the square foot, becomes 

p = m = ^Il(o.oSo7 + -^y, .... (4) 

or, expressed in inches of water, 

/ = 0.19/ = 0.19^^(0.0807 + y)' * . . (5) 

The loss of head, as found by Peclet,* may be expressed by 
the equation 

,,=.^(,3 + 2^^ (6) 

in which / is the total length of flue from boiler to chimney- 
top, in its hydraulic mean depth, or area divided by perimeter, 
and V the velocity of flow in feet per second. When this head, 
h', is given we obtain 



'V— *«' <'> 

13 H -;— 



* Traite de la Chaleur, vol. i. 



1 



THE DESIGN OF THE STEAM-BOILER. 321 

and the weight of gas discharged must be 

ze/ = ^ • — -; ....... (8) 

7", being the temperature of flue. 

The head, h, producing flow is obviously the difference be- 
tween the weight of chimney gases and that of the column of 
air of equal height outside ; or, if T^ is the temperature of the 
latter, 

k = H'^.^^^--H = H[o.^-A. (9) 

^ 0.080; +^ \ ^ ' 

H= /^-f-(o.965- _ ij (10) 

The velocity of flow is measured by a V h, a being a con- 
stant to be found by experiment, or by 



= a////(o.96^i-,), 



(") 



varying as the quantity y (0.96^ — i ); while the density 
varies as i ~ T^, and the weight flowing per second varies as 
the product of velocity and density, or as--|/(o.967; —T^). 

This becomes a maximum, T^ varying, as first indicated by 
Peclet,"^ when 



and 





d. 


Vo.g6T, - 7; 




du 


T. 


= = 

2.083, 


dx 




dl\ 
7; 0.96 



(13) 



* Peclet, vol. i. p. 166. 



322 THE STEAM-BOILER. 

or, as Rankine states it," T^-^T^^^\^, nearly; and the most 
effective draught, but not the most economical, is obtained 
when the absolute temperature of the fiue-gases is 2.08 
times that of the atmosphere, or, as clready stated, ordinarily 
about 550° Fahr. (288° Cenc.) above that of the latter, and 
their density is about one half that of the atmosphere, and 
the volume discharged about twenty-six feet per pound. For 
maximum efificiency of apparatus and economy of fuel the 
temperature must be made as low as possible. 

In constructing grates for boilers the air-spaces should be 
made as narrow as is practicable, the bituminous coals requir- 
ing more air-space than anthracite. A half-inch is usually con- 
sidered a minimum and three fourths a maximum. The area 
of grate should be somewhat more for wood than for coal, the 
same power being demanded. 

158. The Size and Design of the Chimney, its height 
and area of flue, are modified somewhat by its form and pro- 
portions, and by the character of its interior surfaces. The 
greater the friction-head the less its effectiveness. A chimney 
of circular section and with a straight uniform flue is better 
than with any other section or with less direct flue. The flue- 
area is either uniform or tapering toward the top, in which 
latter case the area for calculations is measured at the top. 
Mr. Kent assumes that the friction may be taken as equivalent 
to a reduction of section of two inches all around, and a square 
flue section as equivalent to a circular one of diameter equal to 
its side.f He thus obtains the following : Assuming a commer- 
cial horse-power to demand the consumption of 5 pounds of 
coal per hour, we have the following formulae : 

O.zHP 
E = -^-^A-o.6VA^ (I) 

HP=7,.Z^EVH; (2) 

s=i2VE + r, (3) 

d= 13.54^/^ + 4; (4) 

^-( ^^)^-- ... ..(s) 

* Steam-engine, p. 289. 

f Trans. Am. Soc. M. E. 1884. 



I 



THE DESIGN OF THE STEAM-BOILER. 



323 



in which //P= horse-power ; 77= height of chimney in feet; 
E = effective area, and A = actual area in square feet ; 5= side 
o*f square chimney, and ^=dia. of round chimney in inches. 
The following table* is calculated by means of these formulae : 

SIZES OF CHIMNEYS AND HORSE-POWER OF BOILERS. 



n«5 
"7 V 




Height of Chimneys, 


AND C 


OMMERCIAL HORSE- 


Po 


kVER. 




Hi 


Kff'tive 
Area, 
sq.feet. 


'^it 


.2-5 


50ft 


60 ft 


70 ft. 


Soft. 


90 ft. 


100 ft. 


IIO ft. 12: 


ft. 


150 ft. 


175 ft. 20c 


)ft. 


l<i 


18 


23 


25 


27 














. 






16 


0.97 


1-77 


21 


SS 


38 


4t 






















19 


1.47 


2.41 


24 


4Q 


.S4 


.S« 


62 




















22 


2.08 


3-14 


27 


6,S 


72 


7« 


83 




















24 


2.78 


3-98 


30 


84 


92 


100 


107 


113 


















27 


3.58 


4.91 


.S3 




115 


125 


133 


141 


















30 


4.48 


5-94 


3t) 




141 


152 


163 


T73 


182 
















32 


5-47 


7.07 


3Q 






183 


196 


208 


219 
















35 


6.57 


8.30 


42 






216 


231 


245 


25« 


271 














38 


7.76 


9.62 


48 








311 


330 


34« 


365 


89 












43 


10.44 


12.57 


S4 










427 


449 


472 


03 


551 








48 


13-51 


15.90 


60 










530 


565 


593 (■ 


332 


692 


748 




54 


16.98 


19.64 


66 












694 


728 ' 


76 


849 


918 c 


)8t 


59 


20.83 


23.76 


72 












835 


876 c 


34 


1023 


1 105 I 


8t 


64 


25.08 


28 . 27 


78 














1038 1: 


07 


1212 


I3I0 I^ 


po 


70 


29-73 


33. 18 


«4 














I214 15 


94 


1418 


I53I 1( 


537 


75 


34-76 


38.48 


QO 














14 


9b 


1639 


1770 zi 


93 


80 


40.19 


44.18 


96 


















187b 


2027 2 


by 


86 


46.01 


50.27 



The external diameter at the base should be one tenth the 
height, unless it be supported by some other structure. The 
" batter" or taper of a chimney should be from y^g- to J inch to 
the foot on each side. 

The thickness of brick-work should be, usually, one brick 
(8 or 9 inches) for 25 feet from the top, increasing -J brick (4 or 
4^ inches) for each 25 feet from the top downwards. If the 
inside diameter exceed 5 feet the top length should be i-^ 
bricks, and if under 3 feet it may be ^ brick for ten feet. 

To find the maximum draught for any given chimney, the 
heated column being 612° F., and the external air 62° : 

Multiply the height above grate in feet by .0075, and the 
product is the draught -power in inches of water. 

For natural draught it is found that the weight in pounds 
of anthracite coal which can be burned on the square foot of 
grate per hour is, as a maximum, for example, under the best 
conditions in marine boilers, 



*" Steam," 1885. 



324 THE STEAM-BOILER. 

i^rzz2 |/^- I, nearly; (6) 

and, under more ordinary conditions, 

F=. i.sV~H- I (7) 

From this we obtain the following : 

Heights of Chimney and Rates of Combustion. 
Chimney-section = i to -|^ grate-area. 

Fuel, Anthracite. Best Conditions, 

4 
//"= height of chimney in feet ; W=^ weight of coal burned 
per square foot of grate per hour. 
Thus for 

H= 50, W=iy, 

H=^ 65, ^=15; 

H= 80, W=i7', 

H= 100, W— 19. 

These figures represent very exactly the results of Isher- 
wood's experiments'^ with anthracite coals. 

The best Welsh and Maryland semi-anthracites, or good 
bituminous and semi-bituminous coals, should give, as maxima, 

F= 2.25 ^H^ 
and the less valuable soft coals, more nearly 

Thus, average coals of each quality stand, relatively, nearly 
as follows: 

Weight per Sq. Area Grate 
Foot Grate. per Pound. 

Good anthracite coals i.oo i.o 

" semi-anthracite and bitum. 1.05 0.9 

Ordinary low-grade coals, soft 1.5 ■ 0.7 

" " " anthracite 0.9 i.i 

* Trowbridge, Heat and Heat-engines, N. Y., 1874; Isherwood, Researches 
in Engineering. 



THE DESIGN OF THE STEAM-BOILER. 325 

Some of the soft coals will burn still more freely, while some 
anthracites will burn even less rapidly than above stated. The 
figures given may be taken as fair averages. The height of 
chimney being known in advance or settled upon, the total 
quantity of fuel to be burned determines the area of grate. 
This total quantity is known from the chemical constitution of 
the fuel, or by experiment under defined conditions, and from 
the work demanded and the intended efificiency of the boiler, 
as estimated by the methods already described. 

Mr. Lowe, a builder of large experience, finds the following 
good proportions'" for stationary boilers, presumably allowing 
about 30 pounds of w^ater per hour, and 15 square feet of 
heating-surface per horse-power : 

Steam-Boiler Chimneys. 

Heights in feet 50 60 70 80 90 100 

Sq. in. area per H.P 9 8.67 8.34 8.01 7.68 7.35 

Heights in feet no 120 130 140 150 

Sq. in, area per H.P 7.02 6.69 6.36 6.03 5.70 

Heights in feet 160 170 180 igo 200 

Sq. in. area per H.P 5.37 5.04 4.71 4.38 4.05 

Professor C. A. Smith f gives the following formulas for the 
relation of height of chimney to fuel consumption : 

^=f5^y; ^=-5^. F-'^^^- 
\AJ' ^/ff' ^ JT ' 

where H is the height of chimney in feet, A its flue-section 
in square feet, and i^the pounds of coal burned per minute. 

Mr. J. T. Henthorn:}: gives the following tables of dimen- 
sions of chimney as obtained by the empirical formula: 

120G 

\ F 

in which he takes the area, G, of grate in square feet, the 
height, H, in feet, and the area of flue. A, in inches. It is 

'^ Am. Machinist, March 27, 1886. 
\A7n. Engineer, Sept. 21, 1883, p. 123. 
\ Journal of Commerce, July 5, 1884. 



326 



THE STEAM-BOILER. 





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„-as8„^s.K8sa£|yaK8s:aR8gaRj|'Ha£g;SIIH&s:i&§ j 



THE DESIGN OF THE STEAM-BOILER. 



327 



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HE H 



328 



THE STEAM-BOILER. 



assumed, as in common practice, that the plain cylindrical 
boiler on an average will, when supplying a good engine with 
detachable valve-gear, require about 47 square feet of heating- 
surface for actual indicated horse-power, and the tubular boiler 
1 1.8, the two boilers giving 2.1 and 3 horse-power, respectively, 
per square foot of grate. 

The following figure is the graphic representation of the 



.160 1 1 [ 1 1 1 1 1 1 


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o o o o o 

00000 

o 2j 10 2 cJ 

HORSEPOWER: - GRATE SURFACE X 3 H. P. 

Fig. 73.— Dimensions of Chimney. 



law of variation of height with power required or size of boiler, 
as algebraically given in the formula above. 

In building the chimney for ordinary use in connection 



THE DESIGN OF THE STEAM-BOILER, 



329 



with steam-boilers, the fire-brick lining needed, at its lower 
part, when receiving gases from metallurgical or mill furnaces, 
is*not required. The centre-line is fixed on the ground and 
preserved vertical, while under construction, by the use of a 
'' plumb-line," preferably of fine brass wire, with a very heavy 
'' bob" steadied by immersion in a pail of water, molasses, or 
other liquid. 

The shell should rarely be less in thickness than the length 
of a brick at the top, and the lining not less than one half that 
thickness ; this thickness, outside, should be increased by the 
width of a brick at every interval of 50 or 60 feet from the top, 
the lining being kept approximately, as near as may be, at one 
half the thickness of the main wall. 

The great chimney at St. Rollox, Glasgow, of the height of 
4554 feet, has the following dimensions : 



Division 
of the 


Height above 
Ground. 


Outer Diameter 
in Feet. 


Thickness of the Wall in 


Chimney. 


Feet and Inches. 


V. \ 
IV. \ 

III. 

II. 1 
- \ 


435i 
35oi 

2I0i 

ii4i 



I3i 

i6f 

24 

30i 

35 

40 


[ I 

[■ I 

I 

\ ^ 


2 

6 

3 

7i 



The foundation of this chimney has a depth of 20 feet and 
a diameter of 50 feet. It has stood safely and has worked sat- 
isfactorily for nearly a half-century, and may be looked upon as 
a good example of successful construction. 

159. Forms and Proportions of Furnace and Grate 
are settled upon so soon as the character of the fuel and the 
proportions of chimney are fixed. 

The rate of combustion is fixed, as a maximum, as already 
seen, by the height of chimney ; minimum rates are anything 



330 THE STEAM-BOILER, 

less, and the customary rates may be taken as not far from the 
following. 

The rate of combustion of coal in a furnace is usually stated 
in pounds per hour, burned on each square foot of grate. 

Pounds per 
WITH CHIMNEY-DRAUGHT. square foot 

per hour. 

1. The slowest rate of combustion in Cornish boilers. ... 4 to 6 

2. Ordinary rate in these boilers 10 to 15 

3. Ordinary rates in factory boilers 12 to 18 

4. Ordinary rates in marine boilers 15 to 25 

5. Quickest rates of complete combustion of anthracite 

coal, the supply of air coming through the grate 

only 15 to 20 

6. Quickest rates of complete combustion of bituminous 

coal, with air-holes above the fuel -^^ the area of 

grate 20 to 25 

FORCED DRAUGHT. 

7. Locomotives 40 to 100 

8. Torpedo-boats , 60 to 125 

Fuels of the several classes should evaporate, respectively, 
from feed-water at the boiling-point and at atmospheric pres- 
sure, under the most favorable possible conditions, about as fol- 
lows : 



Relatively. 


Weight water 

per unit 
weight of fuel. 


100 


13-5 


no 


15 


80 


II 



Best anthracite 

Best semi-anthracite and bituminous. 

Ordinary coals, soft 

Ordinary coals, anthracite 75 10 

Examples of these several classes are seen in the best 
Pennsylvania anthracites, the Welsh and Maryland semi-anthra- 
cites, or semi-bituminous coals, the ordinary good bituminous 
fuels of Nova Scotia and of Western Pennsylvania, and the 
earthy coals of the West. 

The quantity of steam actually made will depend upon the 
temperature of the feed-water, and will be less as the water is 
colder. It is customary, as elsewhere stated, to reduce the 
results of experiments determining efficiency of boilers to 



THE DESIGN OF THE STEAM-BOILER, 33 1 

" equivalent evaporation from and at the boiling-point," under 
atmospheric pressure. 

.When the maximum possible evaporation is given for feed 
at 212° F. (ioo° C), and at atmospheric pressure, i.e., under the 
standard conditions, multiplying that figure by the reciprocal 
of the factor of evaporation for the proposed temperatures of 
feed and of steam will give the maximum possible evaporation 
under the latter conditions. Thus we get the following : 

RELATIVE EVAPORATION AT VARYING TEMPERATURES OF FEED. 

Temperature of) 212° F. 200 180 160 140 120 100 80 60 40 

feed-water ) 100° C. 93.3 82.2 71. i 60.0 48.8 37.726.615.5 4.4 

Relative steam 



100 98 96 94 92 90 88 87 86 84 

evaporation. 

The coals in common use in the United States are : 

The semi-bituminous coals from Maryland. 

The anthracites from Pennsylvania. 

The bituminous coals from Pittsburg and Western Pennsylvania. 

The bituminous coals from Ohio and the West. 

When burned in ordinary furnaces, these coals will make 
steam, per pound of coal, in nearly the following proportions, 
as given by Mr. T. Skeel :^ 

Semi-bituminous iio 

Anthracite 100 

Pittsburg 90 

Ohio ' 75 

The weights that may be burned on the same grate, with 
the same chimney, will vary nearly as follows : 

Anthracite lOO 

Semi-bituminous 1 20 

Pittsburg 120 

Ohio 200 

Relative areas of grate-surface that will be necessary to 
burn coal enough to furnish the same quantity of steam are 
nearly as follows : 

* Weisbach, Vol. II. 



332 THE STEAM-BOILER. 

Anthracite lOO 

Pittsburg go 

Semi-bituminous 75 

Oiiio 67 

This refers to the average coal of each kind in practice. 

The loss as refuse falling through well-proportioned grate- 
bars may be taken as 5 to 10 per cent for good bituminous 
coals, or 10 to 20 per cent for the lower grades, and about the 
same for anthracites. Wood may be taken by weight as hav- 
ing one half the value of coal. A cord of best hard wood 
should equal a ton of good coal. 

From the results of chemical analyses, the evaporative 
power of various kinds of fuel, expressed in pounds of water 
per pound of fuel evaporated from and at 212° F., which we 
will call E, has average values given by Prof. C. A. Smith^ in 
the following table, which may be found useful, as supplement- 
ary to the several other sets of data already given in this con- 
nection. 

Kinds of Fuel. E 

Pure carbon completely burned to CO2 15 

Pure carbon incompletely burned to CO 4. 5 

CO completely burned to CO2 10.5 

Charcoal from wood, dry 14 

Charcoal from peat, dry 12 

Coke good, dry 14 

Coke average, dry 13.2 

Coke poor, dry, 12.3 

Coal, anthracite 15.3 

Coal, dry bituminous, best o 15.9 

Coal, bituminous 14 

Coal, caking, bituminous, best 16 

Coal, Illinois (from four mines near St. Louis) 12 

Lignite 12. i 

Peat, dry 10 

Peat with one fourth water , 7.5 

Wood, dry 7.25 

Wood with one fifth water 5.8 

Wood, best dry pitch-pine « 10 

Mineral oils, about 22.6 

'^ A771. Ei7gincer, 1883. 



THE DESIGN OF THE STEAM-BOILER, 333 

The anthracite coals burn completely with a thin fire and 
excess of air, but should have a thickness pretty nearly propor- 
tional to the rate of combustion, a good proportion being about 
one foot thickness on a rate of combustion of 20 pounds on the 
square foot of grate per hour (i decimetre per 65 kilogs. on the 
square metre). The bituminous coals will not burn well ex- 
cept in a thick bed and at high temperature, and when re- 
moved from the chilling influence of adjacent cold iron. A 
hot fire and large space for combustion are here essential. 
The furnace may therefore be of less capacity with hard than 
with soft coals ; but a good height over the grate and a large 
combustion-chamber are very desirable with the latter, and are 
of advantage in all cases. A fire-brick furnace, or an arch of 
brick-work over the grate, gives some gain usually. 

The rate of combustion to be anticipated and the intended 
efihciency of boiler, and evaporation per unit weight of fuel 
being ascertained, the area of grate is at once calculable by 
dividing the total weight of steam to be supplied by the evapo- 
ration to obtain the weight of fuel to be needed, and then di- 
viding this total weight per unit of time by the quantity to be 
burned on a unit area of grate. Thus, 1000 horse-power 
being called for, at 30 pounds (13.6 kilogs.) per H. P. per hour, 
30,000 pounds (136 1 kilogs.) of steam are demanded per hour. 
At 10 pounds' evaporation and 10 pounds burned on the square 
foot (48.8 kilogs. on the square -metre) of grate-surface, 300 
square feet (27.9 square metres) of grate must be provided, 
which would usually be divided, for convenience in construc- 
tion and operation, between several furnaces, as furnaces of 
greater depth than about 6 feet (1.8 m.) cannot be easily 
handled, that being about as far as coal can be well thrown ; 
while a greater width than 3 or 4 feet (0.9 to 1.2 m.) introduces 
difificulties of construction. 

The '' combustion-chamber," w^hich usually forms a part of 
a well-designed furnace, may be either simply an enlargement 
of the height of the furnace itself to obtain the space and time 
needed by the gas-currents for complete intermixture and thor- 
ough combustion, or it may be any separate chamber beyond 
the grate. The latter is often the best method of securing the 



334 THE STEAM-BOILER. 

desired results ; but the more usual plan is that of giving con- 
siderable height of furnace-crown. 

Grate-bars are spaced differently for different kinds of fuel. 
Thus, for fine "pea" anthracite coal, the spaces between the 
bars are usually made about a quarter of an inch (0.6 cm.) ; for 
''chestnut," f inch (0.9 cm.); for " stove" coal, ^ inch (1.27 
cm.) ; and for large anthracite and for bituminous coals, f to f 
inch (0.95 to 1.9 cm.); while wood-burning calls for an inch 
(2.56 cm.). 

160. The Relative Areas of Chimney, Flues, and Grate 
are seen to be variable with the circumstances under which the 
boiler is to be operated, but with natural draught and usual 
working conditions certain proportions have become almost 
universally accepted as standard in common practice. Thus 
it may be taken as well settled by experience, that in chimneys 
of circular section, smooth internal surfaces, and in the open, 
where draught is unobstructed by air-currents produced by 
surrounding objects, as, for example, with marine steam-boilers, 
the minimum ratio of chimney-flue section, section through the 
tubes and that over the bridge-wall to grate-surface should be; 
at least, respectively, \, -§-, i, while a maximum to be adopted 
with forced draught is not far from 1, -J-, and \, for anthracite 
coal. The latter ratios will also work well for bituminous, free- 
burning, coals and natural draught ; and the sections may often 
be made still greater, with advantage when a blast is also used 
with such fuel. 

With restricted draught-area the amount of fuel that may 
be burned becomes reduced ; thus, assuming a chimney 50 feet 
(16 m.) high : 

Area of least flue-section (grate = i) ... 0.14 o.io 0.07 0.05 0.04 

Relative coal burned i. 0.8 0.7 0.6 0.4 

Average fuel, lbs. per sq. ft, grate 15 12 10 9 6 

" kilogs. per sq. m 7-5 6 5 4.5 3 

For square sections of chimney-flue and with rough interior 
surfaces the size of chimney is increased both in weight and 
area of section. As a general rule, the height of factory chim- 
neys is increased with the size and number of boilers, irrespec- 



THE DESIGN OF THE STEAM-BOILER. 



335 



tive of the above-stated ratios, and a not uncommon proportion 
of " stack" is that which makes the height about twenty times 
the diameter of the flue. Ordinary mill-chimneys, for moder- 
ate powers, range between 50 and 75 feet (16 and 23 m.) in 
height. 

161. Common Proportions of Boiler are found in ordinary 
practice to be not far from those given below. 

The interior space of the boiler is commonly divided into 
about two thirds or three fourths water-space, the remainder 
being steam-room. In marine boilers more steam-space should 
be given. 

RATIO OF HEATING TO GRATE SURFACE. 

Plain cylinder boilers 12 to 15 

Cornish 15 to 30 

Cylindrical flue 20 to 25 

tubular = 25 to 35 

Marine tubular (fire) 30 to 35 

(water) , 35 to 40 

Locomotive tubular 50 to 100 

The ratio of heating to grate surfaces should, where possible, 
be always carefully determined with reference to maximum com- 
mercial efficiency in the manner described in a later chapter. 

The above proportions produce ratios of weights of fuel 
burned per unit area of heating-surface, in general practice, 
about as follows: 



RATIO OF FUEL BURNED TO HEATING-SURFACE. 



Stationary boilers ... 

Marine (natural draus:ht) 

Locomotive and forced draught 



Pounds per 
sq. ft. H. S. 


Kilogs. per 
sq. in. 


0.5 to 1.0 
0. 5 to 06 
0.8 to 1.0 


O.I to 0.2 
o.i to 0.3 
0.4 to 0.5 



Similarly, the power of such boilers may be reckoned 
roughly as below, and their relative standing in efficiency and 
capacity taken as follows: 



336 



THE STEAM-BOILER. 
HORSE-POWER AND ECONOMY. 





Per H. p. 


Relative Standing. 




Sq. ft. 


Sq. in. 


Capacity. 


Economy, 


Water tube 


lO to 12 

14 to 18 
8 to 12 
6 to 10 

I to 2 


1.0 to I.I 
1.3 to 1.6 
0.7 to I.I 
05 to o.g 
0.1 to 0.2 






Fire-tube 


n •7ir 1 r\ r^ 


Flue 


0.50 
0.20 
0.6 


8 
0.7 
0.8 


Plain cylindrical 

Locomotive 





The above, as with every proportion and detail of the steam- 
boiler, should always be made the subject of careful calculation 
whenever the case is in the least degree peculiar. 

The following are proportions frequently accepted by the 
trade for the two most common varieties of stationary boiler 
sold in the market: 



proportions of cylindrical tubular boilers. 











Flue 


^_ 


Dome. 








Stack. 




"O 


















1 


1 


1 

G 








rt T3 


i 






•a 

s 











<u 


C/2 


1) 







1 

•^5 


■5 O-W 


C/3 

2 


% 


a 
1 


Ij.; 




c 


1 




c 


"SS 


"0 "J 


fc.^ 


c 

T 


4J 


.^^ 









1 JS 




u 








cnt; 


"5t3 











c i- 




a 



a 


ii 

he 

c 


1 

S 


V 

e 

5 




S 






.5'" 
■_> 


X! 

C 

.J 




u 

'53 


§1 


^5^ 


I 


15 


36 


8' IK/ 


30 


3 


8 


20 


20 


H 


% 


3, 


18 


26 


2,950 


5-350 


2 


20 


30 


10' II « 


30 


3 


10 


20 


20 


k 


% 


373 


18 


30 


3i5oo 


5.900 


3 


25 


42 


11' 


3« 


3 


10 


24 


24 




% 


3^^ 


20 


30 


4,400 


7. TOO 


4 


30 


42 


'3' 


38 


3 


12 


24 


24 


35 


% 




20 


30 


5,000 


7,800 


5 


35 


44 


13 


46 


3 


12 


24 


26 


TH 


% 




22 


3b 


5,500 


8,700 


6 


40 


48 


13' 2» 


52 


3 


12 


24 


28 


T5 


% 




24 


3b 


6,400 


9,900 


7 


45 


50 


14' 2" 


52 


3 


13 


30 


30 


T-k 


% 




24 


3b 


6,800 


10.400 


8 


50 


54 


13 2" 


5« 


3 


12 


30 


30 


l^ 


% 




26 


3b 


7,600 


11.500 


9 


60 


54 


16' 2» 


5a 


3 


15 


30 


30 


f? 


% 


4j^ 


26 


45 


8,550 


12.750 


10 


70 


00 


15' 4" 


76 


3 


14 


30 


30 


A^ 


TB 


4}/^ 


28 


45 


10,000 


14,500 


11 


75 


60 


16' 4. 


76 


3 


15 


30 


30 


^2 


TB 


4/^ 


28 


SO 


10.500 


IS. 100 


12 


80 


60 


17' 4" 


76 


3 


16 


30 


36 


s 


TB 




28 


55 


11,200 


16, TOO 


1.3 


qo 


66 


16' 5" 


100 


3 


15 


36 


36 


IB 




32 


55 


13,50c 


19.100 


14 


1 00 


66 


17' 5'/ 


100 


3 


16 


36 


3b 


% 


16 




32 


55 


14,200 


19,800 


15 


125 


72 


17' 6. 


132 


3 


16 


36 


36 


x'b 


M 




36 


60 


17,200 


24,000 



The upright tubular boiler is given less heating-surface 
than the above, is much lighter, and is less economical. The 
locomotive type of stationary boiler has about the same weight 
as the above, but rather less heating-surface. 



THE DESIGN OF THE STEAM-BOILER. 337 

According to Professor Rankine,* a very useful mode of com- 
paring the capacities of different boilers is to divide the boiler- 
space by the area of heating-surface, and thus is obtained 
a mean depth. Of the following examples, the first three are 
given on the authority of Mr. Fairbairn's " Useful Information 
for Engineers:" 

" Mean depth." 
Feet. 

Plain cylindrical egg-ended boiler, with external flues below and 

at each side, but no internal flues 3- SO' 

Cylindrical boiler with external flues, and one cylindrical internal 

flue o i.6s 

Cylindrical boiler with external flues, and two cylindrical internal 

flue i.oa 

Stationary boilers according to Mr. Robert Armstrong's rules . . 3.00 

Multitubular marine boilers, about 0.50 

Locomotive boilers, and boilers composed of water-tubes, aver- 
age about o. 10 

Boilers of large size and capacity exhibit steadiness in the 
pressure of the steam, ready deposition of impurities, space for 
the collection of sediment, and freedom from. priming. Those of 
small capacity excel in rapid raising of the steam to any required 
pressure, small surface for waste of heat, economy of space and 
weight, of special importance on board ship, greater strength 
with a given quantity of material, and smaller damage in the 
event of an explosion. 

Mr. D. K. Clark considers that we may, in ordinary loco- 
motive practice, take the economical consumption of fuel as 
proportional to the square of the area of heating-surface, and 
make the grate-area vary in the same proportion. He adopts 
nine to one as the standard and desirable evaporation of water 
as compared with weight of fuel, makes the maximum and 
minimum allowable rates of combustion 150 and 14 pounds per 
square foot of grate, and the maximum evaporation in loco- 
motive boilers about 22 cubic feet per hour.f A rate of com- 
bustion of 112 pounds is considered a practical maximum, the 
ratio of heating to grate surface being 85 to i. 

* Steam-engine and Prime Movers. 
f Railway Machinery, p. 165. 
22 



338 THE STEAM-BOILER. 

162. The Usual Rates of Evaporation and the effect of 
varying the proportions of tubes has been well determined by 
the experiments of Isherwood and others. 

The proportions of flues and tubes vary somewhat in prac- 
tice ; but it will be found seldom advisable to make tubes more 
than 50 or 60 diameters in length. Where the heating-surface 
consists principally of tubes, the efficiency will be found to vary 
with their length nearly as follows : 

Length of tube (diameters) ... 60 50 40 30 20 

Water per unit weight of fuel : 12 11 10 9 S 

When the ratio of heating to grate area was 25 to i, Isher- 
wood found the evaporation to vary thus : 

Fuel per hour 8 10 12 16 20 24 

Evaporation 105 10. i 9.5 8.2 7.3 6.8 

which series is represented by 

21 
W — 7~z= , nearly. 

Clark obtained with locomotives an equal evaporation with 

Fuel (coke) 15 25 38 56 76 98 125 153 

Ratio of H. S. to G. S 30 40 50 60 70 80 go loo 

the evaporation being constant at 9 of water to i of fuel, which 
may be expressed by 

S = SVF, nearly, 

5" being the ratio of the two areas and F the weight of coke 
burned on the unit of area of grate. 

In estimating area of heating-surfaces the whole surface 
exposed to the hot-furnace gases is reckoned. The formula 
for ef^ciency already given illustrates the progressive variation 
of the evaporative power with change of proportions of boiler. 

163. The Relation of Size of Boiler to Quantity of 
Steam demanded is one that occasionally becomes worthy of 
consideration. Where the steam is required for driving steam- 
engines it is very important that it should be thoroughly dry, 
and it is an advantage to moderately superheat it. Maximum 
economy cannot be attained where wet steam is used. A boiler 



THE DESIGN OF THE STEAM-BOILER, 339 

attached to a steam-engine, and especially where fuel is costly 
and efficiency important, should have ample heating-surface, 
some superheating-surface if practicable, ample extent of water- 
surface area to permit free separation of steam and water, and 
large steam-space. 

Steam employed for heating purposes is not necessarily dry ; 
if may carry a large amount of water with it into the system of 
heating-coils or radiators, and yet give good results, if the 
latter are of large section. Where the pipes are of restricted 
area of section, however, wet steam flowing less freely than 
when dry or superheated, there may result such a retarda- 
tion of flow and of circulation as may cause considerable 
increase of cost. This has been found sufficiently great, in 
some cases, to justify drying, and perhaps superheating, the 
exhaust-steam from engines where used for heating purposes. 
As a general rule, the boiler must be made a trifle larger to 
supply perfectly dry steam and do good work. 

In the use of steam for heating purposes, one square foot 
of boiler-surface w411 supply from 7 to 10 square feet of radiating 
surface. Small boilers should be larger proportionately than 
large boilers. Each horse-power of boiler will supply from 250 
to 350 feet of i-in. steam-pipe, or 80 to 120 square feet of radiat- 
ing surface. 

Under ordinary conditions one horse-power will heat about — 

Brick dwellings, in blocks, as in cities 15,000 to 20,000 cub. ft. 

" stores " " 10.000 " 15,000 " " 

" dwellings, exposed all around 10,000 " 15,000 " " 

" mills, shops, factories, etc 7,000 " 10,000 " '* 

Wooden dwellings, exposed 7,000 " 10,000 " " 

Foundries and wooden shops 6,000 " 10,000 " " 

Exhibition buildings, largely glass, etc 4,000 " 10.000 " " 

The system of heating mills and manufactories by means of 
pipes placed overhead is recommended. 

The air required for ventilation is usually warmed by the 
" indirect" system of radiation, the current passing through 
boxes or chambers in which a sufficient amount of pipe is coiled 
to heat it well. From 5 to 15 cubic feet per individual per 



340 THE STEAM-BOILER. 

minute are allowed, the former in crowded halls, the latter in 
dwellings, and about one tenth as much for each gas-burner or 
lamp. 

164. The Number and Size of Boilers to be used in any 
case in which considerable power is demanded is determined 
mainly by practical considerations related to their construction. 
As a rule, the larger boiler is more economical in first cost and 
in operation, within certain limits, than several smaller boilers 
of equal aggregate power. But passing a hmit which cannot 
be usually very exactly defined, expense is increased, trans- 
portation becomes difficult, location and setting involve prob- 
lems difficult of solution, and management becomes less easy. 
Mr. Leavitt has, however, constructed stationary boilers, of a 
peculiar modification of the locomotive type, of as high as one 
thousand horse-power ; and marine boilers of equal or greater 
power have been built not infrequently for steamers plying on 
the larger rivers of the United States. Stationary boilers of 
100 horse-power and marine boilers of 500 are more -usual and 
more commonly suitable sizes. Locomotive boilers are neces- 
sarily always sufficiently large to supply all the power de- 
manded of the engine. 

The type of boiler has much influence on the limit of size. 
Plain " cylinder boilers" are rarely made more than from 3 to 4 
feet (0.9 to 1.2 m.) in diameter, and this restricts the grate- 
area so that the power derivable from a single such boiler is 
seldom more than 15 or 20 horse-power, and is usually much 
less. The more complex structures often include several fur- 
naces, and yield from 100 to 200 horse-power each on land, and 
more at sea. 

Makers in the United States usually allow 15 square feet of 
heating-surface and one of grate to the horse-power, in plain 
cyhndrical boilers, and the same area of heating-surface, but a 
fourth and a half less grate-area, respectively, with flue-boilers 
and tubular boilers, where estimating for the market. 

M. de Pambour found the priming of French locomotive 
boilers in 1834 to amount to about 30 per cent ; M. de Chatel- 
lier, in 1843-4, found it to be 30 to 50 per cent; but a large 
proportion of the moisture measured was undoubtedly the 



THE DESIGN OF THE STEAM-BOILER. 



341 



product of cylinder condensation, for which loss Clarke al 
lowed as follows : ^ 



Ratio of Expansion. 


Condensation. 








Per cent, of Steam 


Per cent, of 




indicated. 


Total Steam. 


1.25 


12 


II 


1.67 


12 


II 


2 00 


12 


II 


2.50 


21 


17 


3.67 


32 


24 


5.00 


46 


32 


8.33 


73 


42 



— which figures indicate the proportion of steam by weight to 
be added to that calculated for the ideal engine, to obtain the 
probable requirement of the real engine. 

Build'ers of the more economical classes of engines supply 
them with boilers often of less size than the accepted standard 
rating would dictate, as they demand less steam per horse- 
power than the average engine. A good engine of moderate 
size, with an automatically governing and adjusting valve-gear, 
if condensing, should give good results on as low as seven or 
eight square feet of heating-surface per actual horse-power, and 
if non-condensing, with ten or twelve square feet. Large en- 
gines are given a smaller allowance of heating-surface, propor- 
tionally, than are small engines. 

165. The Standard Sizes of Tubes have become well set- 
tled by custom. So large an element of boiler-construction 
necessarily assumes, with time, a somewhat rigid set of propor- 
tions. The sizes employed range from i or \\ inch (25.4 to 
31 mm.) diameter in the smallest boilers, to 2 or 2\ inches (51 to 
63.5 mm.) in the locomotive and other boilers of moderate size; 
and to 3 or 4 inches (76 or 102 mm.), or even 5 or 6 inches (1.27 
or 1.52 mm.), in large boilers, or where a very free draught or 
greater convenience of access are required. Water-tube boilers 



Railway Machinery, p. 144, 



342 



THE STEAM-BOILER. 



are commonly given tubes 4 or 5 inches (102 or 127 m.) in 
diameter. The length of the tube is customarily not above 50 
or 60 diameters in stationary boilers, and two thirds this length 
in marine work. The spaces between the tubes should be about 
one half their diameter ; they are, however, usually placed much 
closer. All tubes in our market are gauged to British measures, 
as below : 

When the dimensions of a tubular boiler are given, the out- 
side diameter of the tubes is usually stated, so that twice the 
thickness must be subtracted to obtain the diameter to be used 
in the calculation of heating-surface. The thickness of tubes 
by different makers varies somewhat, but those given below 
are average values, and can be used without serious error. The 
table gives dimensions of standard sizes of tubes. 



STANDARD TUBES. 



Outside 

diameter in 

inches. 


Thickness in 
inches. 


Internal diameter 
in inches. 


Internal diameter 
in feet. 


Heating-surface in 
square feet, per 
foot of length. 


1.25 


0.072 


1. 106 


0.0922 


0.3273 


I 


5 


0.083 


1-334 


O.III2 


0.3926 


I 


75 


0.095 


1.560 


0.1300 


0.4589 


2 




0.095 


1. 810 


0.1508 


0.5236 


2 


25 


0.095 


2.060 


O.1717 


0.5890 


2 


5 


0.109 


2.282 


0. 1902 


0.6545 


2 


75 


0.109 


2.532 


0.2IIO 


0.7200 


3 




0.109 


2.782 


0.2318 


0.7853 


3 


25 


0. 120 


3.010 


0.2508 


0.8508 


3 


5 


0. 120 


3.260 


0.2717 


0.9163 


3 


75 


0.T20 


3-510 


0.2925 


0.9817 


4 




0.134 


3-732 


O.3IIO 


1.0472 


4 


5 


0.134 


4-232 


0.3527 


I. 1790 


5 




0.148 


4.704 


0.3920 


1.3680 


6 




0.165 


5-770 


0.4808 


1.5708 


7 




0. 165 


6.770 


0.5642 


1.8326 


8 




0.165 


7.770 


0.6475 


2.0944 


9 




0.180 


8.640 


0.7200 


2.3562 


10 




0.203 


9-594 


0.7995 


2.5347 



The following are the dimensions of standard tubes as made 
by some of the best makers in the United States: 



THE DESIGN OF THE STEAM-BOILER, 



343 



LAP-WELDED CHARCOAL-IRON BOILER-TUBES. 
Standard Dimensions. 













1 


1 




1 


1 


o^- 


°-d 










<6 


I 


1 




rt 


J5 


^ c 


ii c 


o" 


1 . 


1 . 


B 
J4 





<-> 


|i 








'— <u 
<U 1 


"^ a 

u T 




1 


SSi 


as 





V 


s ^ 


ev 




^a 


^a 

03 

c 

2 


^i 


a 




5" 






1 


3 >< 


3.H 

'0 




C 


g3 




1 














H 


H 


H 


:i- 


kJ"" 


In. 


In. 


In. 


No. 


In. 


In. 


Sq. in. 


Sq. in. 


Sq. in. 


Feet. 


Feet. 


Lbs. 


I 


.86 


.072 


15 


3-14 


2.69 




78 


■57 


.21 


3-82 


4.46 


-71 


I 125 


.98 


.072 


15 


3 


53 


3- 


08 




99 


.76 




24 


3-39 


3 


89 


.8 


1-25 


I. II 


.072 


15 


3 


93 


3. 


47 


I 


23 


.96 




27 


3-06 




45 


.89 


1.32 


1-15 


-083 


14 


4 


12 


3 


6 


1 


3-2 


1.03 




32 


2.91 




33 


1.08 


1-375 


1. 21 


-083 


14 


4 


32 


3 


8 


I 


48 


1-15 




34 


2.78 




16 


1-13 


15 


1-33 


.083 


14 


4 


71 


4 


19 


I 


77 


1.4 




37 


2-55 




86 


1.24 


1.625 


1-43 


•095 


13 


5 


I 


4 


51 


2 


07 


1.62 




46 


2-35 




66 


I 53 


1-75 


1.56 


■095 


13 


5 


5 


4 


9 


2 


4 


i.gt 




49 


2.18 




45 


1.66 


I 875 . 


1.68 


•095 


13 


5 


89 


5 


^9 


2 


76 


2.23 




53 


2.04 




27 


1.78 


2. 


1. 81 


-095 


13 


6 


28 


5 


69 


3 


M 


2-57 




57 


1.91 




II 


1. 91 


2.125 


1-93 


-095 


13 


6 


68 


6 


08 


3 


55 


2.94 




61 


1.8 




97 


2.04 


2.25 


2.06 


-095 


13 


7 


07 


6 


47 


3 


98 


3-33 




64 


1-7 




85 


2.16 


2-375 


2.16 


.109 


12 


7 


46 


6 


78 


4 


43 


3-65 




78 


1. 61 




77 


2.61 


2-5 


2.28 


.109 


12 


7 


85 


7 


17 


4 


91 


4-09 




82 


1-53 




67 


2 75 


2-75 


2.53 


.109 


12 


8 


64 


7 


95 


5 


94 


5-03 




9 


139 




51 


3 -04 


2.875 


2.66 


.109 


12 


9 


03 


8 


35 


6 


49 


5-54 




95 


1-33 




44 


3-18 


3- 


2.78 


.109 


12 


9 


42 


8 


74 


7 07 


6.08 




'^t 


1.27 




37 


3-33 


325 


3-OI 


.12 


II 


10 


21 


9 


46 


^ 1 


7,12 




18 


1. 17 




26 


3-96 


3-5 


3-26 


.12 


II 


II 




10 


24 


9.62 


^i^ 




27 


1.09 




17 


4.28 


3-75 


3-51 


.12 


II 


II 


78 


II 


03 


II 


04 


9.68 




37 


1.02 




09 


4-6 


4- 


3-73 


• 134 


10 


12 


57 


II 


72 


12 


57 


10.94 




63 


•95 




02 


5-^7 


4-25 


3-98 


•134 


10 


13 


35 


12 


51 


14 


^9 


12.45 




73 






96 


5.82 


4-5 


4.28 


• 134 


10 


14 


14 


13 


20 


15 


9 


14.07 




84 


-85 




9 


6.17 


4-75 


4.48 


• 134 


10 


14 


92 


14 


08 


17 


72 


15.78 




94 


.8 




8s 


6.53 


5- 


4-7 


.148 


9 




71 


14 


78 


19 


63 


17-38 


2 


26 


.76 




81 


7-58 


5-25 


4 95 


.148 


9 


16 


49 


15 


56 


21 


65 


19.27 


2 


37 


-73 




77 


7 97 


5-5 


5-2 


.148 




17 


28 


16 


35 


23 


76 


21.27 


2 


49 


• 7 




73 


8.36 


6. 


5-67 


.165 


8 


18 


85 


17 


81 


28 


27 


25 25 


3 


02 


.64 




67 


10.16 


7- 


6.67 


.165 


8 


21 


99 


20 


95 


38 


48 


34-94 


3 


54 


-55 




57 


II. 9 


8. 


7.67 


.165 


8 


25 


13 


24 


I 


50 


27 


46.2 


4 


06 


.48 




50 


13-65 


9- 


8.64 


.18 


7 


28 


.27 


27 


14 


^3 


62 


58 . 63 


4 


99 


.42 




44 


16.76 


10. 


9-59 


.203 


6 


31 


.42 


30 


14 


78 


54 


72.29 


6 


25 


•38 




4 


20.99 


II. 


10.56 


.22 


5 


34 


-56 


33 


17 


95 


03 


87-58 


7 


45 


-35 




36 


25-03 


12. 


11-54 


.229 


4-5 


37 




36 


26 


"3 


I 


104.63 


8 


47 


•32 




33 


28.46 


13- 


12.52 


.238 


4 


40 


.84 


39 


34 


132 


-73 


123-19 


9 


54 


.29 




3 


32.06 


14. 


13-5 


.248 


3-5 


43 


.98 


42 


42 


153 


•94 


143.22 


10 


71 


.27 




28 


36- 


15- 


14.48 


259 


3 


47 


. 12 


45 


5 


176 


7^ 


164.72 


II 


99 


-25 




26 


40^3 


16. 


15-43 


.284 


2 


50 


.26 


48 


48 


201 


.06 


187.04 


14 


02 


24 




25 


47.11 


17- 


16.4 


-3 


I 


53 


.41 


51 


52 


226 


.98 


211.24 


15 


74 


.22 




23 


52-89 


18. 


17-32 


-34 





56-55 


54 


41 


254-47 


235-61 


18.86 


.21 


.22 


63.32 



The following table"^ gives the draught-areas of boiler-tubes 
and flues, which have been computed on the basis of the thick- 
ness of such tubes taken from the price-lists of American manu-' 
facturers : 



American Em^iiieer, \\ 



344 



THE STEAM-BOILER. 



DRAUGHT-AREAS OF TUBES AND FLUES. 









Number of 


External diam- 


Draught-areain 


Draught-areain 


tubes or flues 


eter in inches. 


square inches. 


square feet. 


=• I square foot 






.0040 


ofdraught-area. 


I 


•575 


250.0 


li 


.96S 


.0067 


149-3 


li 


1.389 


.00964 


103.7 


If 


1. 911 


•0133 


75-2 


2 


2.575 


.0179 


55-9 


2i 


3.333 


.0231 


43-3 


2i 


4.083 ' 


.0284 


35-2 


2f 


5-027 


•0349 


28.7 


3 


6.070 


.0422 


23.7 


3i 


7. 116 


.0494 


20.2 


3i 


8.347 


.0580 


17.2 


3l 


9.676 


.0672 


14.9 


4 


10.93 


•0759 


13.2 


4i 


14.05 


.0976 


10.2 


5 


17.35 


.1205 


8.3 


6 


25.25 


■1753 


5-7 


7 


34-94 


.2426 


4-1 


8 


46.20 


.3208 


3-1 


9 


58.63 


.4072 


2.5 


10 


72.23 


.5016 


2.0 



In a flue-return tubular boiler the area of flues should be 
about 20 per cent, and the draught-area of uptake about 25 per 
cent greater than the draught-area of tubes. Good conditions 
for combustion and steaming are realized when the grate-sur- 
face is 8 times and the heating-surface about 200 to 240 times 
the draught-area of tubes. 

The location and arrangemienc of fire-tubes has an impor- 
tant bearing on the distance by Avhich they may be safely 
separated. In locomotive boilers, where they only check 
the rise of currents laden with steam produced by their own 
action, they may be set closer than in those boilers, as many 
marine boilers, in which they lie above a crown-sheet from 
which enormous quantities of steam are liberated, which steam, 
as well as that made by the tubes themselves, must traverse 
the intermediate spaces. Where the circulation is forced and 
rapid the tubes may also be crowded more than where natural 
and sluggish. In locomotive boilers, the tubes, which are or- 
dinarily from if to 2 inches in diameter, are set apart from 



THE DESIGN OF THE STEAM-BOILER. 345 

one third to one fifth their diameters ; but the larger space is 
probably none too great. 

• 166. The Details of the Problem, as coming to the de- 
signer and the constructor of the steam-boiler, are so largely 
matters determined by experience, rather than by any scientific 
system or calculation, that much thought must be given to 
their consideration from the point of view of the practitioner 
in engineering and of the artisan engaged in building such 
structures — from the boiler-maker's side rather than from that 
of the man of science. 

The selection of the iron or steel for shell, for stays, or of 
the rivets; the choice of style of riveting; the determination 
of the character of seam and lap ; the decision of the question 
whether the use of reinforced seams or of heavier plates is 
likely to prove best in the end ; the choice of type of boiler 
even, in view of known peculiarities of location or other 
conditions : these must all be settled in conference with the 
boiler-maker, even if not directed absolutely by him. It sel- 
dom happens that the engineer making the designs feels com- 
petent to act throughout without consultation with his lieu- 
tenants in the workshop. 

The method of designing in its details, as practised in the 
case of familiar forms of boiler, will be given in the next 
chapter. 



CHAPTER VIII. 

DESIGNING STEAM-BOILERS — PROBLEMS IN DESIGN. 

167. The General Considerations determining the design 
of a steam-boiler are, mainly, the following : 

(i) It must supply a defined quantity of steam in a speci- 
fied unit of time, or it must have a certain power. 

(2) It must be as absolutely safe as it is practicable to 
make it. 

(3) It must have reasonably high efficiency, and must be 
capable of working at the lowest total expense for fuel, attend- 
ance, interest on first cost, taxes, insurance, and all other run- 
ning expenses, in proportion to work done, that may be attain- 
able. 

(4) It must be well suited to the location, and to all the 
special conditions affecting it when in operation. 

Marine steam-boilers must, for example, be given the mini- 
mum practicable weight and volume, since it costs as much to 
carry a ton of boiler as a ton of cargo, and every cubic foot 
occupied by boilers, fuel, or machinery displaces a cubic foot of 
paying load. Naval boilers, also, must usually be kept as low 
in the ship as possible to reduce risk of injury by shot. So 
important are these elements in naval construction, that the 
practical limits of space and power on shipboard are com- 
monly fixed by the space occupied by boilers ; and the reduc- 
tion of grate-area is the first problem attacked by the naval 
architect and engineer seeking high speed, whether for yachts, 
torpedo-boats, or larger craft. 

168. The Parts and Details of the steam-boiler may be 
defined as follows :^ 

* See Rankine, Steam-engine, p. 449. 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN. 2>A7 

The usual arrangements of furnace and boiler may be 
divided into three principal classes : 

'(I.) In the external furnace, or " outside-fired boiler," the 
furnace is wholly outside of the boiler ; so that the boiler 
iorms part of the superficies of the furnace ; the other sides of 
the furnace being usually of fire-brick. Examples of this are 
the wagon boiler, the plain cylindrical boiler without internal 
flues, and all boilers in which the water and steam are con- 
tained in tubes surrounded by the flame. 

(II.) In the internal-furnace or " inside-fired boiler" the 
fire-chamber is enclosed within the boiler, as in boilers with 
furnaces contained in horizontal cylindrical internal flues, in 
most marine boilers, and in all locomotive boilers. 

(III.) The detached furnace, which is a fire-chamber built 
of fire-brick, in which the combustion is completed before the 
gas comes in contact with the boiler. 

The principal parts and appendages of a furnace are — 

(i) The furnace proper, or firebox, being the chamber in 
which the solid constituents of the fuel, and the whole or a 
part of its gaseous constituents, are consumed. 

(2) The grate, which is composed of alternate bars and 
spaces, to support the fuel and to admit air. 

(3) The hearth is a floor of fire-brick, on which, instead of 
on a grate, the fuel is burned in some furnaces. 

(4) The dead-plate or dumb-plate, that part of the bottom 
of the furnace which consists of an iron plate simply. 

(5) The mouth-piece, through which fuel is introduced, and 
often some air. The lower side of the mouth-piece is the dead- 
plate. In many furnaces there is no mouth-piece. 

(6) The fire-door closes the doorway, and may or may not 
have openings and valves in it to admit air. Sometimes the 
duty of a fire-door is performed by a heap of fuel closing up 
the mouth of the furnace. 

(7) The furnace-front is above and on either side of the 
fire-door. 

(8) The ash-pit is the space into which the ashes fall, and 
through which, in most cases, the supply of air enters. 

(9) The ash-pit door is used to regulate the admission of air. 



34^ THE STEAM-BOILER. 

(lo) The bridge is a low wall at the end of the furnace over 
which the flame passes to the chimney. This is meant when 
''the bridge" is spoken of ordinarily; but the word bridge, or 
bridge-wall, is also applied to any partition having a passage 
for flame or hot gas over it. Bridges are of fire-brick, or of 
plate iron and hollow, so as to form part of the water-space 
of the boiler, and are then called water-bridges. The top of 
a water-bridge should slope upwards at the ends to allow of 
the rapid escape of the steam on its internal surface. A 
water-bridge may project downwards from the boiler above 
the furnace ; it is then called a Jianging bridge. 

(ii) Th.Q co7nbustioii ox flame-chamber is the space behind 
the bridge in which the combustion of the furnace-gases is 
completed. It may be lined with brick or tile to prevent ex- 
tinction of the flame. 

(12) Bafflers or diffusers are partitions so placed as to pro- 
mote the circulation of the gas over the heating surface of the 
boiler or of the currents of water within. Bridges fall under 
this head. 

(13) Dampers are valves placed in the chimney, flues, or 
passages to regulate the draught. 

The principal parts and appendages of a body are : 
(i) The ^//^// of the boiler. The figures usually employed 
for the shells of boilers are the cylindrical and the plane, and 
combinations of those two figures. In locomotive boilers, 
part of the shell is a rectangular box, containing within it the 
firebox. The shells of marine boilers are often of irregular 
shapes, adapted to the space in the ship which they are to 
occupy, and approximating more or less to rectangular forms. 
For heavy pressures, however, they are usually cylindrical, with 
plane ends. 

(2) The steam-chest, steam-drum, or dome is a part which 
rises above the rest of the boiler, and provides a space in 
which the steam may deposit any spray carried by it; it is 
usually cylindrical. 

(3) The furnace or firebox is usually within the boiler, so 
placed as to be covered with water. In cylindrical boilers it is 
often in one end of a horizontal cylindrical flue, as in Cornish 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN. 349 

boilers ; in locomotive boilers it is a rectangular box. In 
marine boilers it is usually rectangular in the older kinds of 
boiler, and cylindrical in the high-pressure cylindrical tubular 
boiler. 

(4) A tube-plate forms part of the shell of the boiler, or one 
side of an internal firebox, or flue, and is perforated with 
holes, into which the ends of the tubes are fixed. Each set 
requires a pair, one for each end of the tubes. 

(5) The man-Jwle is an opening in the top or end of the 
boiler, large enough to admit a man. The bolts holding the 
man-hole cover must be capable of safely bearing their load. 
Commonly the cover opens inwards, and is kept' closed by the 
pressure of the steam, and is held by bolts and nuts to a cross- 
bar outside the man-hole. 

(6) Hand-holes are openings usually placed at or near the 
lowest part of a boiler, and large enough to admit the hand, 
which are opened occasionally for the discharge of sediment. 

(7) The blow-off apparatus consists of a cock at the bottom 
of the boiler, which is opened to cleanse the boiler by empty- 
ing it or to discharge brine, and prevent salt from collecting. 
The surface blow-cock discharges the scum which collects on 
the surface of the water. 

(8) The pressure-gauge shows the pressure within the 
boiler. 

(9) The water-gauge shows the level of the water in the 
boiler. Gauge-cocks are set at different levels : one at the 
proper water-level, another a few inches above, and a third a 
few inches below. Opening these the engineer ascertains the 
level of the water. The glass water-gauge consists of a strong 
glass tube, communicating with the boiler above and below 
the water-level. The level of the water is thus rendered visi- 
ble. Every boiler ought to be provided with both forms of 
gauge. 

(10) Clothing and lagging prevent waste of heat. The 
former is made sometimes of hair felt, the latter covers it with 
a layer of thin wooden boards. Asbestus, ashes, and other ma- 
terials are similarly used. Hair-felt has sometimes been found 
to singularly accelerate internal corrosion. 



350 THE STEAM-BOILER. 

169. The Design of the Plain Cylindrical Boiler is the 

simplest problem of its class. This boiler, consisting of only 
a cylindrical shell and plane or domed heads, is not likely to 
afford opportunity for the display of either great knowledge in 
design and construction or of ingenuity in its details. This 
type is selected when cheap fuel or bad water make it unwise 
to adopt more economical forms. 

The shell is usually about twelve diameters in length, but is 
sometimes made fifteen or even twenty, and double the last fig- 
ure has been known. In some cases this boiler has been built as 
a cylindrical ring — an annulus of large diameter and of circular 
section. Common sizes for this class of boiler range from 24 
to 36 inches (63 to 91 cm.) diameter of shell, and 24 to .36 feet 
(7.3 to II m.) long. As the diameter of the boiler usually fixes 
the wadth of grate, and as the length of grate is rarely found to 
be profitably extended beyond about 6 feet (1.8 m.), the power 
of the boiler has a very simple relation to its size. The ratio 
of heating to grate surface is always thus made small, and the 
boiler is necessarily uneconomical of fuel. 

This boiler is usually designed with single-riveted seams 
throughout, although safety and even ultimate economy of 
cost and operation during its lifetime may be sometimes gained 
by double-riveting the longitudinal seams ; which would thus 
be strengthened in the proportion of about 70 to 55 or 60, 01 
not far from 20 per cent, and the whole structure would be 
made correspondingly safer. 

The thickness of shell is determined by the pressure of 
steam to be carried and the factor of safety adopted. Assum- 
ing the iron to have a tenacity of 50,000 pounds per square 
inch (3515 kilogs. per sq. cm.), the joints will have, as may be 
assumed, 0.60 this resisting power, and the boiler-shell is to be 
calculated with this loss in mind, and will be made as if the 
sheets had a tenacity of 30,000 pounds per square inch (2109 
kgs. per sq. in.), and were of uniform strength through the 
seams. In illustration, assume it to be demanded that a '^ 36- 
inch cylindrical boiler" shall be designed to sustain a pressure 
of 100 pounds per square inch (7 kilogs. per sq. cm.). The 
thickness of shell should be. 



DESIGNING STEAM-BOILERS— PROBLEMS LN DESIGN. 35 1 

_ fpd _ 6 X loo X 3^ ._ « 

— 2/^r~ 2 X 0.55 X 50,000 ~ *' 

when /, d^ and Z are the pressure and the diameter of the 
shell and the tenacity of the metal, and k is the'' efficiency" of 
the seam, which we may here assume to have /& = 0.55, or 55 
per cent of the strength of the solid sheet; the factor of safety 
is taken as/"^6. The thickness of shell should be three- 
eighths of an inch (i cm. nearly). Such thickness is not usual, 
and a factor of safety of four and a thickness of one quarter of 
an inch (0.635 cm.) is more common for this case in general 
practice, and is allowed by the law as may be seen in article 
55, to which reference may be made for tabulated legal dimen- 
sions of this class of boilers. 

The heads of the cylindrical boiler are sometimes made of 
cast-iron, the thickness made empirically from \\ to 2^ inches 
(3.8 to 6.4 cm.) for diameters of from 24 to 36 inches (63 to 91 
cm.) respectively ; they are often of sheet-iron of the same 
thickness as the shell, and domed to give them resisting power, 
— an excellent construction, especially when pressed into exact 
shape in the forming die of the hydraulic press. When the 
heads are plane, they are stayed either by stays running to the 
sides of the boiler at angles of from 10° to 30°, or by triangu- 
lar "gusset-plates" riveted to the heads and sides. This last 
construction is subject to the objection that the gusset-plates 
are necessarily irregularly strained and liable to tear. Stay- 
rods are of sufficient size to safely carry the whole pressure re- 
ceived on the heads, and securing both heads, pass from the 
one to the other, the whole length of the boiler, with adjust- 
able nuts at each end, outside the head, and inside as well. 

A dished head is probably the best form to give, whether of 
boiler, of dome, or of steam and mud drums. As shown by 
Mr. Robert Briggs,* equal strength with the shell or with a 
stayed head can be obtained by giving the proper form to the 
head-sheet without any staying. Thus it is known that the 
strength of a spherical shell is twice as great as that of the 

* Journal Franklin Institute, 1878. 



352 THE STEAM-BOILER. 

cylinder of the same diameter, when both shell and cylinder 
have the same thickness ; or that a spherical shell possesses 
the same strength as a cylindrical shell of the same thickness,, 
when the radius of the spherical surface is equal to the diame- 
ter of the cylinder. When the rule stated is applied to the 
head of the dome or of the boiler, which is formed to a part of 
a spherical surface whose radius is the diameter of the dome or 
boiler, the head is "dished" out 0.134 the diameter of the 
head, in order to give the same strength to resist internal pres- 
sure, for both head and shell, of the same thickness of iron. A 
small allowance is needed for the thinning of the sheet-iron, in 
disJiing. This allowance is easily computed thus : The sur- 
face of the flat circular plate is to that of the dished plate as 
I to 1.072, and the thickness of the circle, before dishing, should 
be about 7 per cent (one fourteenth) greater than that of the 
shell. The flangeing of the head will inevitably upset the flange 
itself to a thickness much above the original ; and a dished head 
of ordinary thickness will be much stronger than the shell 
sheets at the joints, where they are weakened by rivet-holes, 
even if put together with the double-riveted longitudinal 
seams. 

Heads of sheet-iron are usually made ten or, better, twenty 
per cent heavier than the shell. 

A man-hole is commonly located in the most accessible end 
of the boiler, and, often, a hand-hole through which the boiler 
may be completely drained, and all mud and scale removed. 
The feed-pipe usually enters through the front head, but some- 
times at the rear. It should always be at a part readily reached 
for inspection and repairs. If on the shell, the opening should 
always be reinforced by a heavy wrought-iron ring and the 
strength of the boiler thus increased rather than diminished by 
its introduction. The ring should be riveted inside the open- 
ing. The steam-pipe is sometimes led directly out of the top 
of the boiler, but is better placed in connection with a steam- 
dome or steam-drum, in order to obtain as dry steam as is pos- 
sible. The safety-valve should here, as in all other cases, be so 
placed that no accident or carelessness can close its communi- 
cation with the steam-space ; a stop-valve placed between it 



DESIGXIXG STEAM-BOILERS— PROBLEMS IN DESIGN. 353 

and the boiler has been known to produce a disastrous explo- 
sion, when shut by an ignorant or thoughtless attendant. 

Gauge-cocks should always be attached even if the glass 
water-gauge is in use. The experienced manager of boilers, 
never feels perfect confidence in any other water-level indicator^ 
however convenient and generally accurate. In setting the 
gauge-cocks it is usual to allow about one third the volume 
of the boiler for steam-space. The following table, calculated 
by Mr. W. F. Worthington, gives the volume of this space in 
unity of length of the shell, British measures: 



TABLE FOR CALCULATING THE CAPACITY OF THE STEAM 
CYLINDRICAL BOILERS. 



SPACE IN 



DiAM 


30 " 


32" 


34" 


36" 


38" 


40 " 


42'/ 


48 V 


54" 


60 « 


66-/ 


72-. 




In. 


Multipliers (cubi 


c feet). 










In. 


)h' I 


■05 


•05 


•05 


•05 


.05 


.06 


,06 


.06 


.06 


.07 


.07 


.08 


I 


^ 2 


• 14 




14 




15 




15 




16 


.i6 




16 




17 


.19 




20 


.21 




21 


2 


1 3 


•25 




26 




27 




28 




29 


■30 




30 




32 


•34 




37 


•38 




39 


3 


>.- 4 


•39 




40 




42 




43 




44 


•45 




46 




50 


•53 




55 


• 58 




61 


4 


I ^ 


•53 




56 




57 




59 




61 


•63 




64 




69 


•73 




78 


.82 




85 


5 


% 6 


.70 




72 




75 




77 




80 


.82 




83 




91 


.90 


I 


02 


1.08 


I 


12 


6 




.87 




90 




93 




96 




99 


1 .02 


I 


05 


I 


14 


1.20 


I 


27 


1-35 


I 


41 


7 


o g 


1.05 




09 




13 


I 


17 


I 


20 


1.24 


I 


27 


T 


37 


1.47 


I 


55 


1.63 


I 


71 


^ i 


« 9 


1.24 




29 




33 


I 


38 


I 


42 


1.47 


I 


51 


I 


62 


1^73 


I 


85 


1.94 


2 


04 


9 r^ 


B. lo 


1^43 




49 




55 


I 


59 


I 


65 


1.70 


I 


75 


I 


89 


2.02 


2 


14 


2.26 


2 


38 


10 % 


7! II 


1.63 




69 




76 


I 


82 


I 


89 


I 95 


2 


00 


2 


18 


2.33 


2 


46 


2.59 


2 


74 


II ._ 


£ 12 


i^83 




91 




98 


2 


06 


2 


'3 


2.20 


2 


26 


2 


46 


2.63 


2 


79 


2-95 


3 


08 


12 c 




2.04 


2 


13 


2 


21 


2 


30 


2 


38 


2.46 


2 


53 


2 


75 


2.93 


3 


12 


3-31 


3 


46 


liH 


2.24 


2 


35 


2 


44 


2 


53 


2 


63 


2 72 


2 


80 


3 


04 


325 


3 


47 


3^67 


3 


85 




2 


57 


2 


68 


2 


79 


2 


89 


2.98 


3 


08 


3 


35 


3^6t 


3 


84 


4-05 


4 


26 


15 £ 


^ i6 






2 


92 


3 


03 


3 


15 


3.26 


3 


37 


3 


66 


3^94 


4 


19 


4-43 


4 


6j 


16 4, 


^ I? 








3 


28 


3 


41 


^•53 


3 


65 




98 


4 29 


4 


57 


4-83 


5 


09 


17.5 


^ ^8 










3 


67 


3^8i 


3 


93 


4 


30 


4.63 


4 


95 


5^23 


5 


53 


18 1 


5 19 












4.08 


4 


22 


4 


63 


5.00 


5 


32 


5^66 


5 


97 


19 ^ 


■ji 20 














4 


52 


4 


96 


5^35 


5 


72 


6 08 


6 


41 


20 ^ 

21 ^ 


Q 21 
















5 
5 


28 
61 


5^72 
6. 10 


6 
6 


12 
51 


6.50 
6.92 


6 

7 


84 
30 




22 B 




5 95 


6.46 


6 


92 


7-35 


7 


76 


23 £ 






6.82 


7 


33 


1-19 


8 


24 


24 « 






7.20 


7 


75 


8.22 


S 


71 


25 g 






7-57 


8 


15 


8.70 


9 


20 


26 § 


Rule.— Multiply the number in the table by the 






8 
8 


57 
97 


9.14 
9^59 
10.04 
10.49 


9 
10 


68 

67 
16 


27 .2 

28 Q 
29 
30 


length of the boiler in feet, and the product will be 






g 


10 


the capacity of the steam-space in cnbic-feet. 








II 










10.94 


11 


62 


31 










11-39 


12 
12 
13 


12 
62 
12 


32 
33 
34 












1363 


35 



In designing this, as any other boiler having a cylindrical 
shell and fired externally, it is advisable to secure as large 
23 



354 THE STEAM-BOILER. 

sheets, and as few seams on the under side and where exposed 
to the action of the fire and the furnace gases, as possible. 
Boilers are now often made with but a single sheet extending 
from end to end, and of such width that all longitudinal seams 
are above the reach of flame. 

The steam-space should be of such volume that the varia- 
tion of pressure produced by each stroke of the engine should 
be unimportant. An old rule given by Bourne made the space 
not less than twelve times the volume of steam taken out by 
the engine at each stroke ; it may, however, be less for a given 
power as the speed of rotation of the engine is higher and as 
the ratio of expansion is increased. Tredgold would restrict 
the variation of steam-pressure at each stroke to about three 
per cent of the normal amount, which would, if V be the 
volume of steam-space of the boiler, 5 that of the single cylin- 
der, up to the point of *' cut-off," and r the ratio of expansion, 
adopting Tredgold's coefficient, 0.033, 

r — I 
F=30 5. 

For coupled engines, a much smaller space may be al- 
lowed. 

According to Shock,* marine boilers of the older types 
work dry when they contain in their steam-space a supply suf- 
ficient for the engine during 14 seconds and give wet steam if 
the steam-space is sufficient for but 12 seconds ; while the more 
modern forms of high-pressure boilers will only furnish dry 
steam when containing a volume equal to 20 seconds' supply. 
Steam-space of considerable altitude is most effective. 

170. Stationary Flue-boilers are designed, as to dimen- 
sions of shell, very much as are plain cylindrical boilers. 
They are commonly of somewhat larger diameter and of com- 
paratively less length. 

The Cornish boiler, in which the single great flue serves also 
as furnace, is rarely made of less than 6 feet (1.8 m.) in diame- 
ter, as a smaller flue than that so obtained gives too contracted 

* Steam-toilers, p.' 306. 



DESIGNING STEAM-BOIIERS— PROBLEMS IN DESIGN. 355 

a furnace. The length of this boiler is usually from 25 to 40 
feet {j.6 to 12 m.). The thickness of shell is made about \ inch 
(1.27 cm.) and of flue f inch (0.95 cm.) for the shorter and |- 
iiich (1.27 cm.) for the greater length, the steam-pressure 
adopted being usually about 40 pounds per square inch (3 at.). 
Both should, however, be carefully computed by the methods 
already given (§§ 55, 56), and a good factor of safety — not less 
than 6 — is advised to be adopted and permanently maintained. 
The flue is nearly always one half the diameter of the shell. 
Where the boiler is long, and the flue thus becomes structurally 
weak, strengthening rings, or flanged girth-seams, should be 
adopted to insure greater strength and safety in the flue, which 
should, because of its special liability to injury and general, as 
distinguished from local, failure, be even safer against collapse 
than the shell against bursting. Collapse of the flue, however, 
is less likely to be disastrous to life and surrounding property 
than explosion of the shell. The heads are so well stayed by 
the flue that they require no other bracing below the water- 
line ; above that level, however, they should be stayed by ei- 
ther stay-rods or gusset-pieces, like the plain cylindrical boiler. 
The same remarks also here apply, relative to appurtenances of 
the boiler, as in the preceding case. 

Multiflue Boilers are constructed either with or without 
fireboxes. The latter will be considered more at length in 
later articles. Flue-boilers without fireboxes are simply com- 
posed of a cylindrical shell with plane heads, and having flues 
running from end to end, below the water-line, and secured in 
the heads, at each end, by means of flanges turned in those 
*' flue-sheets" and riveted to the ends of the flues. These 
flanges are usually turned inwards, but are sometimes on the 
exterior, the projecting end of the flue, extending beyond the 
plane of the head. The number and size of these flues is de- 
termined mainly by the judgment of the designer, and no rule 
exists ; but the better the water used and the more valuable 
the fuel consumed, the more numerous the flues. Where two 
are put in, they are commonly about one third the diameter of 
the boiler, each, and are set side by side below the horizontal, 
diametral line of the shell. When more are used, the number 



356 



THE S TEA M-B OILER 



is first increased to five, each of about one fourth the size of 
the boiler-shell. With still further subdivision the designer 
puts them in as he best can, ordinarily keeping their centres at 
the intersections of horizontal and vertical lines, set apar' dis- 
tances equal to the diameter of flue plus the desired space for 
circulation, which varies from one half to one fourth the diam- 
eter of the flue accordingly as the latter are more or less nu- 
merous. Ample room for circulating currents is no less essen- 
tial to ef^ciency than extent of heating-surface, and, as a matter 
of safety, more so. Small flues are commonly made of iron of 
the same, or somewhat less, thickness with the shell, and, when 
numerous, have an excess of strength over that indicated by 
calculation and a correspondingly increased margin for safety.. 




Fig. 



-Flue with Rings, 



Flues of sizes below 5 or 6 inches (1.5 or 1.8 cm.) diam- 
eter are not usually riveted up, as is the case with the larger 
flues, but are commonly drawn in the tube-rolling mill and are 
known in the market as tubes. The larger mills also often pro- 
duce drawn tubes, or flues, of much larger size ; some, handled 
by the Author, have been as large as 16 inches (4.9 cm.). 
In consequence, partly, of such changes in modern facilities for 



DESIGNING STEAM-BOIIERS— PROBLEMS IN DESIGN. 357 

construction, and for various other obvious reasons, the tubu- 
lar has very generally superseded the flue boiler. Where still 
used, it is customary to allow about 12 square feet (1.16 
sq. m.) of heating surface per horse-power, and not far from 
20 to I as the proportion to grate-surface. 

Fig. 74 illustrates a case in which the flues are strength- 
ened by rings, placed at the girth-seams joining each adjacent 
pair of ring-courses. 

The domestic make of corrugated flue now used in the 
^' Scotch" marine boiler is illustrated in the following engraving. 




Fig. 75.— The Corrugated Flue. 



In this class of boiler it proves particularly valuable, since 
the construction here met with, of high steam-pressure and 




Fig. 76. — Form of Corrugated Flue used as Furnace in Marine Boiler. 

a forced fire, is one which demands strength of structure, and, 
at the same time, compels the use of thin iron. One objection 



358 THE STEAM-BOILER. 

to this form of flue is found in its liability to become encrust- 
ed with scale or with sediment in the corrugations. 

Fig. 76 shows the form given the corrugated flue when 
constructed for use as a furnace in a marine boiler, and as 
made by Mr. Fox, who first successfully manufactured them. 
The joints are welded in a gas-flame, and are usually but little, 
if at all, weaker than the solid sheet. 

For good stationary boilers, according to Cave,"^ about 4 
pounds of steam may be allowed as the evaporation to be ex- 
pected per square foot of heating surface (19 kgs. per sq. m.) ; 
but this quantity is very variable with the form and proportions 
of the boiler, locomotive boilers producing several times this 
quantity, and the am.ount so evaporated increasing generally 
as the efficiency of the generator diminishes. The Cornish 
boiler, as formerly customarily operated, supplied but about one 
fourth the above-mentioned quantity of steam. 

171. The Cylindrical Tubular or Multitubular boiler Hke 
the flue boiler, may be made either with or without firebox ; 
it is now most frequently made " plain," consisting of a cylin- 
drical shell, with plane heads and a " nest " of tubes fitting and 
nearly filling the water-space up to the water-level. The com- 
mercial and accepted rating and proportions of this class of 
steam-boiler have already been given in § 161. In all impor- 
tant work, the designing engineer will carefully determine the 
size and economical proportions for the special case in hand. 
The following may be taken as illustrating the process for this 
case, as well as for boilers generally : 

It is required to design a tubular boiler or a set of boilers 
capable of supplying steam to a condensing engine of 500 horse- 
power, guaranteed to demand not more than 22 pounds (10 
kgs.) of steam per H. P. per hour, the pressure to be 100 pounds 
per square inch (6J atmospheres), and the feed-water to be 
taken from the condenser at 120°. Fahr. (48°. 8 C). 

The first step is to determine the quantity of steam to be 
made. Calculation on the above basis would make it ii,ooa 
pounds (4990 kgs.) per hour, evaporated from 120° Fahr. (48°. 8 

* Traite des Machines a Vapeur; Bataille et JuUin. 



DESIGNING STEAM-BOILERS— PROBLEMS LN DESIGN. 359 

C.) at 338° Fahr. (170° Cent.) as shown by the steam-tables 
(Appendix, Table I.). At the customary rating, however (30 
pounds or 13.6 kgs. per horse-power), the weight to be evapo- 
rated would be 15,000 pounds (6804 kgs.) per hour, and this 
larger figure is taken as permitting a good margin. Were this 
evaporated by the best fuel and in a boiler having the efficiency 
unity, it would require the supply of 1000 pounds {4536 kilogs) 
of coal per hour. 

The financially desirable efficiency of the boiler should be 
next determined as indicated in the chapter devoted to that 
subject ; it may be here assumed to have been found to be 
0.75 ; and 1333 pounds (6048 kgs.) of fuel would be demanded 
per hour. By the use of the expression already found (§ 98) 
we have 

B 

E = 0.75 = 



in which we may take ^ = 0.5 and B = i ] then 

and 

S=2F. (2) 

Thus the best ratio of heating to grate surface is twice the 
number representing in British measures the quantity of fuel 
burned on the unit area of grate. It thus becomes necessary 
as a next step to ascertain this last quantity, and therefore to 
ascertain the height of chimney. This is, in the case of con- 
siderable power, as here, to be determined by the principles de- 
tailed in §§ 157 and 158. A height of 125 feet may be 
taken as the result of this investigation. A well-designed 
chimney of this altitude should permit the combustion of 15 
pounds per square foot (7.5 kgs. per sq. m.) of grate with a mar- 
gin of at least one third for contingencies. On this basis, the 



3^0 THE STEAM-BOILER. 

area of grate must be 82 square feet {'j.6 sq. m.) and the area 
of heating surface 2460 square feet (228 sq. m. nearly). This 
is to be distributed among two or more boilers ; since, although 
a thousand horse-power, even, may be, and sometimes is, ob- 
tained from a single boiler, it is usually found inexpedient to 
concentrate power to such an extent. 

A boiler of 5 feet (1.5 m.) diameter and 2\ or 3 diameters 
long has become a very common and very satisfactory size. 
This permits a grate of about 30 square feet (2.8 sq. m.), and 
three such boilers having grates 6 feet (1.8 m.) in length would 
give the required grate-area with an allowance of ten per cent 



Fig. 77.— Tubular Boiler. 

for ineffective surface along the edges and in the corners. It 
may be taken as a good rule to throw in all such differences 
on the side of increased boiler-power. A boiler of this charac- 
ter with 3-inch {j.6 cm.) diameter of tube will be found to have 
63 square feet (5.9 sq. m.) area of heating-surface per unit 
length, and a length of 15 feet (4.57 m.) gives very exactly the 
desired total area for a single boiler. The proportion of length 
of tube to diameter, 60 to i, is considered a good one, although 
rather high ; and such a boiler operated under the assumed con- 
ditions would supply the power demanded with the intended 
economy of fuel. 



^ 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN. 361 

The tube-sheets would be made, if of steel, a half-inch (1.27 
cm.), or a little less, in thickness, to give good holding power, 
and the shell, if of metal having a tenacity of 60,000 pounds 
per square inch (4218 kgs. per sq. cm.), would be, if double- 
riveted in the longitudinal seams, as in Fig. J^j, f inch (0.95 
cm.) in thickness. The tubes would be 66 or 68 in number, 
and the braces of sufficient number and strength to sustain 
the heads safely. The dome would be probably given about 
one half the diameter of the boiler, and be made of metal rather 
more than one half as thick, as it would usually be single-riv- 
eted. 

The tubes should always be placed in vertical and horizon- 
tal rows; to ''stagger" them would insure a defective circula- 
tion and injury to those thus exposed to overheating. 

The tubes should never be nearer than 3 inches to the 
shell of the boiler, and should never be carried down near the 
bottom of the boiler ; but there should be ample water-space 
at the bottom of the shell. The fire from the furnace first 
strikes the bottom of the boiler, and there should be a good 
body of water there. 

Pressures have risen in stationary-boiler operation until the 
common cylindrical tubular boiler of 6 feet (1.8 metres) di- 
ameter is made \ inch (1.27 cm.) in thickness of shell, and is 
safe, with usual construction, at a pressure of nearly ten at- 
mospheres. 

172. Marine Flue-boilers are rarely used at sea, but remain 
in use on the rivers of the United States. In their design, the 
same principles which have just been applied are also applica- 
ble in the determination of the dimensions of shell and flues. 
The firebox forms an essential feature of this class, however ; 
and its construction involves calculations of strength of stayed 
surfaces. In the locomotive, the stay-bolts are placed 4 or 
5 inches (10 to 12.7 cm.) apart, but in marine boilers they are 
more widely distributed, as working pressures are lower. In 
any case, the area of the flat surface should be estimated, and 
also the pressure upon it, and a sufficient number of braces 
used to provide for that pressure. If the braces are of iron of 
known strength, say 60,000 pounds per square inch (3515 kgs. 



3^2 THE STEAM-BOILER. 

per sq. cm.), a factor of safety of lo would give 6,000 pound? 
(or 422 kgs.) on each brace of unit section, and the number of 
braces should be sufficient to safely carry the load on the total 
surface. The heavier the plate, the greater its resistance to the 
distorting action of the steam-pressure, and the heavier the 
stay-bolts and the wider their spacing. In the older forms of 
marine flue-boiler, in which steam-pressures ranged from 25 to 
40 pounds per square inch (if to 2f atmos.), the stay-bolts were 
usually spaced from 10 to 8 inches(25 to 20 cm.) apart, and were 
given a diameter of from one eighth to one tenth those figures.. 
This form of boiler has so generally been superseded by the 
tubular boiler that it has now comparatively little importance,, 
except on the large rivers. The following are the proportions 
adopted on board a number of Ohio and Mississippi river 
steamers, all of which use the lap-welded and drawn tube in 
place of the older form of riveted flue : A steamer on the 
Ohio has two boilers, 47 inches diameter and 24 feet long,, 
ten lap-welded flues in each, of 8 inches diameter; two 
boilers 41 inches diameter, 24 feet long, with six lap-welded 
flues in each, of 10 inches diameter ; steamer Golden Rule,, 
three boilers, 44 inches diameter, 26 feet long, with three 8- 
and three lo-inch lap-welded flues in each. Such flues are more 
cylindrical in form than the riveted flue, thereby lessening the 
chances of collapsing. There are no rivet-heads or laps to in- 
terfere with the draught, and consequently the flues are not li- 
able to choke up with soot, are much less apt to scale, and hav- 
ing smooth surface, are much more easily cleaned. 

The water-level should be at least 6 inches (2.4 cm.) above 
the highest flue, and is usually fixed by law or regulation at a 
minimum of 4 inches (1.6 cm.). The highest line of heating- 
surface is usually required to be below that level. Where ex- 
posed to flame these boilers are not allowed to have a thick- 
ness exceeding 0.51 inch (1.2 cm.), and a water-space of at least 
3 inches {j.6 cm.) is left between the flues and between flue 
and shell. 

173. The Marine Tubular Boiler has now almost univer- 
sally been brought to a very definite standard form and propor- 
tions. It has been already described as consisting of a cylin- 



DE SI a XING STEAM-BOILERS— PROBLEMS IN DESIGN. 363 

drical shell with plane heads, traversed by large flues and 
comparatively small tubes, the furnaces being in the flues. 
Those designed for sea-going steamers are often of very large 
diameter, the steam-pressures often exceeding ten atmospheres 
(150 pounds per square inch), they are also made of very heavy 
boiler-plate. These boilers naturally are oftener double- 
riveted than those of smaller diameter, and every expedient 
known to the engineer is adopted to insure safety. Diameters 
of 15 and even of nearly 20 feet (4.6 and nearly 6 m.) are com- 
mon, and plates as thick as i\ inches (3.2 cm.) have been used. 
These heavy plates are usually butted at the seams, and the 
joint is covered with a " butt-strap" or " covering-strip," double- 
riveted on each side, thus presenting to the eye four parallel 
rows of large rivets. The calculation of the shell is made in 
the same manner as in the cases of the forms of boiler already 
considered. The size is determined partly by the conditions 
and the method described in § 171, and partly by the necessity 
of getting the whole set of boilers into a space limited both as 
to volume and form by the construction of the vessel and by 
the necessity of economizing as much as possible that space 
which might be otherwise used for lading and passengers. The 
stays are usually long rods, extending from end to end in the 
steam-space, and screwed stay-bolts, reinforced with nuts, in 
the water-spaces. The dimensions of a steel and of an iron 
boiler of this class, as actually constructed, are, as given by the 
builders, the following: 



STEEL BOILER FOR 6 ATMOSPHERES (90 Lbs. Pressure). 

Diameter, 16 ft.; length, 11 ft.; shell, | in. thick. 

4-9 m-; " 3.35 m.; " 2.2 cm. " 

3 Furnaces, 48 in. diameter; -i| in. '* 

1.2 m. " 1.3 cm. " 

250 Tubes, 3I in. " 6^ ft. long 

7.7 cm. " i.gS m. 

Area heating-surface 1800 sq. ft. (167 sq. m.). 

Weight of boiler 70,000 pounds (31,750 kgs.) nearly. 

water 50,000 '* (22,680 " ) " 

T-^tal weight 120,000 " (54.430 " ) " 



3^4 THE STEAM-BOILER. 



IRON BOILER (Same Pressure). 

Diameter, 14.7511.; length, 11 ft.; shell, li in. thick. 

4-5m.; " 3.35 m.; "2.86 cm. 
3 Furnaces, 39 in. diameter; i| in. " 

0.99 m. " j»3 cm. " 

258 tubes, 3^ in. " 7 ft. long. 

8.9 cm. " 2.1 m. long. 

Area heating-surface 2000 sq. ft. (186 sq. m.). 

Weight of boiler 75, 000 pounds (34,088 kgs.) nearly. 

'' water... 45,000 " (20,412 kgs.) " 

Total weight ..120,000 " (54,430 kgs.) •* 



The drawings herewith given, Fig. 78, illustrate the details 
of this construction. Marine steam-boilers require peculiar care 
in their design and construction. They must be as light and as 
small as is possible consistent with the efficiency demanded, 
and, being exceptionally liable to rapid corrosion and general 
deterioration, much depends on their being so made as to per- 
mit every precaution to be taken to prevent such injury and 
to insure their preservation. In the construction of cylindrical 
shells the longitudinal seams are usually all double-riveted, 
and often even butt-jointed, with double covering strips: this 
is almost always done in cases in which very high pressures 
compel the use of heavy plates. 

In ordinary practice, the heating-surface ranges from 30 to 
40 times the grate-area ; the evaporation ranges from 6 or 8 to 
10 or II pounds per pound of good coal consumed ; the crown- 
sheets are carried as high above the grate as the form of boiler 
allows ; the grate bars are inclined about one in twelve, from front 
to rear, and are given a length as little more than 6 feet as is 
practicable. In the cylindrical mar;ne boiler, in which the 
grates must be set in furnaces which form the lower and larger 
set of flues, it is not possible to secure either as good a propor- 
tion of grate, or as great height above it as is desirable ; and 
the inefficiency sometimes noticed in boilers of this class is 
commonly due to these faults of the furnaces. 

174. Sectional and Water-tube Boilers differ as radically 
in their design and construction, as in type, from the shell- 



1 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN 3-65 




Boiler with Corrugated Flue. 



!.. 


-^^^y 




Three-furnace Boiler. 



Fig. 78.— Marine Steam-boilers 



366 THE STEAM-BOILER. 

boilers which have been here considered. As a rule, their de- 
sign involves but little calculation of strength, as their tubes 
and connections are always vastly stronger than is absolutely 
necessary as a mere matter of supporting the steam-pressure. 
The '' headers " or other connections of parts are commonly 
without rivets, and are fitted, piece to piece, with machine- 
made '* faced " joints, and held in place by bolts. Some special 
precautions are demanded, in designing this type of boiler, to 
secure safety against injury, and to avoid serious difficulties 
arising in management from the comparatively small body of 
water and of steam carried by them, and the consequent ab- 
sence of the self-regulating power observed in shell-boilers. 

Mr. Robert Wilson states that the following appear to be 
the points that require special attention in designing these 
water-tube boilers, to insure their satisfactory working and 
durability : 

(i) To keep the joints out of the fire. 

(2) To protect the furnace-tubes from the sudden impinge- 
ment of cold air upon them on opening the fire-door. 

(3) To provide against the delivery of the cold feed-water 
directly into the furnace-tubes. 

(4) To provide for a good circulation to take away the 
steam from the heating-surfaces. 

(5) To provide passages of ample size for upward currents 
so that they may not interfere with downward currents. 

(6) To provide passages of ample size, for steam and water, 
between the various sections of the boiler, to equalize the pres- 
sure and water-level in all. 

(7) To provide ample surface of water-level to permit the 
steam to leave the water quietly. 

(8) To provide a sufficiently large reservoir for steam to 
prevent the water being thrown out by suddenly opening a 
steam or safety valve. 

(9) To provide against the flame taking a short cut to the 
chimmey, and impinging against tubes containing steam only. 

The several forms of this type of boiler now becoming fa- 
miliar have illustrated great ingenuity in securing efficient and 
novel arrangement of parts, rather than special knowledge of 



DESIGNING STEAM-BOILERS— PROBIEMS IN DESIGN. 367 

the chamcter and strength of materials. Some of these forms 
liave been already described, and need not be here further il- 
lustrated. This class of boiler is generally in use on land, but 
attempts have been made to introduce them for marine pur- 
poses. 

The Author has under his hand sets of drawings of marine 
tubular boilers for a naval vessel, and of a "sectional" water- 
tube boiler intended for similar power and the same duty, which 
afford a means of comparing standard designs of the two types. 
It does not follow, however, that this comparison would in all 
cases yield similar deductions. 

The tubular boiler has a shell 9 feet (2.74 m.) in diameter, 
while the other is only 5 feet (1.52 m.). The tubular has i^ inches 
{3.2 cm.) thickness of metal between fire and water where the rear 
tube-sheet sets into the shell ; the greatest thickness in the sec- 
tional boiler, between fire and w^ater, is only \ of an inch (9.5 
mm.). The shell-boiler has a ratio of grate-surface to heating-sur- 
face of I to 23, and the ratio of grate-surface to calorimeter is 7.2 
to I ; the sectional has a ratio of grate to heating surface of i to 
41.3, and a ratio of grate-surface to calorimeter of 4.82 to i, 
which means the ability to burn more coal per unit of grate- 
surface. 

The steam-space is practically identical in both, but the 
water in the tubulars weighs 12.6 pounds against 15.5 pounds 
in the sectional. 

The total iron-work of the tubular boilers is 35!- pounds per 
;sq. ft. of heating-surface, whereas in the sectional it is 25.8. 
The total weight per unit of heating-surface is as 48 in the 
former to 41 in the latter. The tabular comparison on page 
368 was presented at the same time. 

On the other hand, it is objected, by those who oppose the 
introduction of these boilers on shipboard, that the following 
considerations are too important to permit their safe employ- 
ment."^ 

(i) That they usually occupy as much space as shell- 
boilers. 

* Shock's Steam-boilers, pp. 280-1. 



368 



THE STEAM-BOILER. 





Shell Tubulars. 


Sectional. 


Shell 


9 ft. diameter X 9 ft 
% in. thick. 


7 in 


long, 


5 in. diameter X 20 ft 
thick. 


long, 


%in- 




Heads . 


% in. thick. 
■J/i in. thick. 


r.° 


carry ( 
5 lbs. f 


Ml in. tliick. 
None 


( To c^rrv 


Seams in fire 


\ 150 


lbs. 


Heatin,o--surface 


1322.7 sq. ft. 






3100 sq. ft. 






Grate surface 


57.3 sq. It. 


^i 


x; 


75 sq. ft. 


8i 


<u 


Ratio of grate-surf'e 




"?2 


1 




°°2 


be 


to heatingf-surface. 


I sq. ft. to 23 sq. ft. 


^« 




I sq. ft. to 41.3 sq. ft. 


!^bJo 


i/i 


Steam-space 


169 cubic ft. 

S .012 cubic ft. per i ( 






392.6 cubic ft. 

\ .012 cubic ft. to I 1 

1 sq.lt. f 




oi 


Ratio of steam-space 


id 


•^1 




a 


to heating-surface. 


■) .'^q. ft. f 


If 


^S* 


Ci 


Water, weight of.. .. 


16,660 pounds 


i'i 


48,262 pounds 


»4 


oJ "^ 


Weight per .sq. foot 




H°°- 


d^ 




"2^ 


heating-surface. . . 


12 6 


"1^ 




15-5 " 


' flT 


^^ 


Iron-work, weight of 


47,040 


£^^ 


80,221 " 


b^ 


« 2 


Iron-work per sq. ft. 




w U 


<ti.c 




^x. 


N^S 


heating-surface 


35-5 " 


ti 3 


Os^ 


25 8 


^5 




Total weight.. 


63.700 " 


^k 




128,423 " 


•^S) 


tn U 


Total weight per sq. 




•a.S 


ess 




T3 C 


^^ 


ft. heat-surface 


48.18 


11 


§g.8 


41.44 


%^ 


C n3 

c a 


Calorimeter 


8.27 sq. ft. 


HJ 


V ^ 


18 sq. ft. 


¥.\ 




Ratio of grate-sur- 




c^ 


'i.^'^i 




£;"« 


face to calorimeter. 


7.2 to I sq.ft. ■ 


^'^X'^O'^ 


4.82 to 1 sq. ft. 


^"^x 


Su^- 


Height of water-line 








6"z 


^ 


above crown-sheet. 


6 in. 






24 in. 


in f 





(2) That they are subject to rapid and serious fluctuations 
of water-level and steam-pressure. 

(3) That the circulation is less free and steady. 

(4) That, for the above reason and because of their liability 
to accumulation of incrustation, overheating is sometimes pe-- 
culiarly apt to take place. 

Notwithstanding these objections, which are undoubtedly 
to a certain extent valid, these boilers are thought likely, by 
^ many engineers, to find their Avay into use at sea. 

Every good " sectional " boiler consists of a system of water- 
tubes, or their equivalent, so arranged as to permit a rapid, 
steady, and certain circulation ; a system of ^' headers " or con- 
nections by which the steam and water find their way into the 
steam-space, where separation and settling may occur ; and of 
this steam-space, usually in the shape of a large drum or set of 
drums of small section from which the steam is discharged, dry, 
into the steam-pipe, and by it conveyed to the point at which 
it is to be utilized. In some cases, the steam-drum is also 
partly a water-reservoir, and thus assists in producing a regu- 
larity of operation very difficult to secure unless obtained by 
the presence of a considerable body of water, somewhere in the 
structure. In this last case, the greatest care must be taken to 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN. 369 

secure this drum against the direct action of flame, the nest of 
tubes being ordinarily so disposed as to intercept the gases 
leaving the furnace. 

175. Upright and Portable Boilers are chosen when the 
location or use is such as demands concentration of space or 
facility of transportation. The upright boiler, occupying little 
floor-space, having, for the small powers for which it is most 
commonly used, no great height, and being self-contained and 
thus requiring no setting, is a form that meets these special 
conditions most perfectly. Its design is precisely that, in 
method, of the cylindrical tubular boiler, except that it must 
have a firebox. The latter is made in the form of a short cy- 
lindrical, upright, flue, occupying so much of the lower part of 
the boiler as will give the needed height of furnace and ash- 
pit. The water-space between this flue and the shell is usually 
about one tenth the diameter of the latter. 

In the design of this flue or furnace, care should be taken 
to introduce stay-bolts to prevent collapse from overpressure 
or weakness produced by corrosion, a method of yielding which 
causes the greater proportion of explosions of boilers of this 
kind. The thickness of furnace sides is commonly the same as 
that of the shell ; the bottom ring and the tube-sheet, at its up- 
per end, giving additional security and making the furnace very 
much safer against accident so long as it is in good order.. 
The calculations of this detail are the same as for any other cy- 
lindrical flue subjected to external pressure. 

The steam -space in the upright boiler, as often built,, 
consists only of the volume of the upper part of the boiler 
above the water-level, and as the tubes occupy a considerable 
proportion of the total volume of the shell, the steam-space is 
correspondingly restricted. This extension of the tubes above 
the water-level to the upper tube-sheet also renders their upper 
ends liable, at times, to injury by overheating. A better plan 
is that shown in § 15, in which the upper tube-sheet is sunk be- 
low the water-level, and all the steam-space needed is obtained 
by carrying the shell upward to any desired additional height, 
and connecting the two by a frustum of a cone having its upper 
end no larger than is needed for the chimney-flue ; the tubes. 
24 



370 



THE STEAM-BOILER. 



are thus protected, and the steam-space made ample. The 
same remarks apply to the computations of this cone as to 
those of the furnace ; it is, however, of stronger form and less 
likely to require staying. 

The Portable Boiler is sometimes upright, as when used by 
itself independently of the engine, or when it has to carry the 
frame of an upright engine ; or it is horizontal, if of large size, 
or if forming the bed-piece of a horizontal engine, as is a more 
common arrangement. In either case, no very important dif- 
ference arises in either the design or method of construction, 
except that somewhat greater care is taken to make it safe 
against injury either by transportation or by the stresses com- 
ing of the action of the attached machinery. It is always bet- 
ter that the boiler should carry an engine with its frame than 
that it should itself act the part of that member. In all cases, 
the connection of engine and boiler and of boiler with its car- 
riage, where locomotive, should be so arranged that the changes 
of form and dimension due to variations of temperature and 
the stresses caused by difference of temperatures of adjacent 
parts as well as changes of pressures may have no ill-effect. 

A good steam-drum or dome is of even greater advantage 
on the portable than on the stationary boiler. Their attached 
engines are usually wasteful, take steam in very variable quan- 
tity, and are peculiarly liable to cause '' foaming." 

The following are the proportions adopted for portable 
engine-boilers by a well-known firm of British builders : * 



PORTABLE ENGINE-BOILERS. 





Heat-surface— Square Feet. 


Grate-surface. 


Grate- 
surface. 


Tubes. 




Horse- 
power. 


Fire- 
box. 

19.6 
32-4 
43.0 
53-0 


Tubes. 

81.8 
161. 9 
228.7 
279.2 

340-5 
408.8 


Total. 


Per 
Horse- 
power. 


Total. 


Per 
Horse- 
power. 

0.72 

0.62 

0.53 
0.52 
0.51 
0.49 


Heat- 
surface. 


Draught- 
way — 
Sq. ft. 


Horse, 
power. 


5 

lO 

15 
20 
25 
30 


101.4 
194-3 
271.7 

332-2 

405-8 
476.9 


20.2 
19.4 
16.9 
16.6 
16.0 
15-9 


3-6 
6.2 
8.6 
10.5 
12.8 
14.9 


28.2 
31-1 
31.6 
31-7 
31-8 
31-9 


0.66 
1.08 

1-39 
1.60 
1.87 
2-35 


5 
10 

15 
20 

25 
30 



* Wansbrough, p. 81. 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN. 37 1 

A source of danger to which the upright boiler is pecuharly 
hable is that of "burning" the firebox or tube-sheet in conse- 
quence of the collection of sediment in the water-legs about the 
furnace or on the lower tube-sheet. The water-leg is sometimes 
found filled with solid matter, and the tube-plate so heavily in- 
crusted that the metal is readily overheated and burned. All 
boilers of this kind should be provided with hand-holes at the 
level of the crown-sheet of the furnace, and so placed as to 
permit thorough inspection and complete removal of the sedi- 
ment at frequent intervals. 

Comparing the vertical with the horizontal tubular boiler, 
it will be observed that a large item of expense is avoided in 
the cost of setting ; and that an incidental advantage is secured 
for the former in the fact of its accessibility at all times, 
whether working or cold, for examination of the exterior. The 
upright boiler is also less liable, while in operation, to injury 
from a small depression of the water-level ; the fire never comes 
in contact with its shell, and this permits the safe use of plates 
as heavy as may be desired ; no strains from unequal expansion 
are to be apprehended, and experience shows this to be an ele- 
ment contributing to the exceptional durability of this class of 
boiler. Its only setting is a foundation with an ashpit, and its 
connection to the chimney-flue. In the vertical tubular boiler, 
loss of water, and the falling of the water-level even a consid- 
erable proportion of the whole depth of boiler, does not neces- 
sarily involve danger ; and the upper part of the tubes may be 
utilized as superheating surface, and the extent of the super- 
heating adjusted very conveniently by varying the water-level. 

Where the feed-water is not very pure, however, the great 
and often fatal objection to this form of boiler arises in the 
danger of sediment or scale being deposited on the lower tube- 
head, the furnace-crown, and introducing danger of overheating 
and of explosion. A considerable proportion of the explosions 
of this kind of boiler, which have been investigated, are known 
to have been due to this cause. 

176. ** Locomotive " Boilers whether stationary or actually 
forming a part of the locomotive, are of the same general design 
and construction. They consist of a horizontal, cylindrical, 



372 THE STEAM-BOILER. 

tubular boiler, crowded, as far as is safe and practically eco- 
nomical, with tubes, and with a firebox added as an integral 
part of the structure. In such boilers, designed to be station- 
ary, the tubes are often larger than those adopted in the 
boiler of the locomotive, as the draught is commonly vastly 
less intense, and the power demanded also comparatively small. 
The boiler of the locomotive represents the highest art of the 
eno^ineer in the combination of the essential desiderata for its 
purpose : great power in small weight and volume, combined 
with maximum economy of fuel consistent with such concen- 
tration of power. 

The locomotive must always use steam of maximum 
pressure, must use enormous quantities because of its neces- 
sarily great power, and must be at once safe and fairly econom- 
ical. In consequence of its exposure to the action of its own 
great inertia in its constant motion over, often, an irregular 
roadbed, and because it must sustain the stresses due to the 
action of its own machinery and to frequent collisions, of 
greater or less violence, while making up and transporting 
trains, the whole structure must be designed with especial re- 
gard to such extraordinary and unreckoned strains as may be 
thus caused. Since the power demanded is a maximum, the 
tubes must be as numerous, and therefore as small and as 
closely packed, as is possible without affecting sensibly the 
circulation of water and thus losing steaming capacity ; 
and since economy of fuel is hardly less important than steam- 
ing capacity, the tubes must have sufficient length to give a 
ratio of area of heating surface to weight of fuel burned such as 
will insure that efficiency found to be practically desirable. 
With all this, the designer must keep in mind the special ne- 
cessity of compactness of structure, and of a limit in weight 
fixed, in many cases, at least, by the magnitude of the friction 
on the rail and the tractive power demanded by the special 
kind of work for which the engine is intended. To reconcile 
so many and oftentimes conflicting conditions, and to secure 
a maximum total efficiency, is evidently a problem of immense 
importance and of corresponding difficulty, and one which can 
only be fully solved by the gradual evolution of the precise 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN. 373 

form and proportions best fitted for each of a number of spe- 
cialized types and duties, such as is illustrated by the different 
passenger and '' freight " or " goods " engines now becoming 
standard. 

The methods of computation of size and strength of parts 
are in no way peculiar, and no special consideration of them is 
here demanded. Custom guided by experience has led to the 
production of such proportions as are illustrated in standard 
practice. 

Common faults of design in this, as in other forms of hori- 
zontal tubular boilers, are the excessive crowding of tubes and 
serious contraction of the water-spaces about the furnace. It 
would probably be found advantageous not only to preserve 
good water-channels between adjacent tubes, but to leave out 
a vertical row of tubes along the diameter of the boiler, and to 
allow an equal space between the nest of tubes and the shell 
all around. This has often been done by good constructors, 
with evident advantage, when boilers are doing much work. 
It is a safe- arrangement to adopt for all cases. Water-legs 
should be made to widen from the bottom upward. 

The crown-sheet is supported by girders, " crown-bars," rest- 
ing at each end on the upper edge of the side sheets of the 
furnace and carrying the load by stays set at frequent intervals 
in their length. They should be very carefully designed. 
Stays to the shell are unsafe. 

The material used in this class of boiler is becoming univer- 
sally soft steel, containing so little carbon that it will not tem- 
per. Harder steels crack in the firebox-sheets, especially where 
deep and hard-worked. The thickness of the shell is often re- 
duced 15 or 20 per cent, as compared udth iron. Good steel 
neither cracks nor blisters. As a rule, with steam at 120 pounds, 
the general practice is, in the United States, to use |-inch iron 
or steel for outside sheets, -f^ inch iron or steel for fireboxes, 
and from f to -J inch for tube-sheets. Water-spaces around 
firebox from 2\ to 3^ inches inside, and from 2f to 4 inches in 
front. At straight seams \^ inch rivets are used, spaced if 
inches between centres. Longitudinal seams double-riveted, 
centres of the two lines of rivets ij inches apart, centre to cen- 



374 THE STEAM-BOILER, 

tre of rivets on same line 2f inches. Stay-bolts f inch di- 
ameter, 4 inches centre to centre. It is thought that thin 
plates give the best result in fireboxes, sides and back of 
i-inch steel, crown-sheet y^g-inch steel, and tube-sheet f inch. 
Tube-sheets of y^g-inch iron, the other plates being steel, have 
also given good results. It is believed that ^-inch steel plates 
are strong enough for side sheets and less liable to crack than 
thicker plates. Crown-sheets are more easily straightened 
when sagged down from mud collecting, and will not crack 
so quickly from overheated crown-bar bolts.. 

The life of a good boiler is usually from ten to twelve years. 
Tubes are removed to permit inspection every three or four 
years. Steel and iron are now used for wood-burning fireboxes, 
with a result usually declared to be in favor of steel, in conse- 
quence of the lighter sheets and the metal not blistering. 
With bituminous coal copper, steel, and iron are used. Copper 
will not crack, but wears away, and is soon reduced to a dan- 
gerous thinness. A copper firebox lasts from three to five 
years. The objection to iron fireboxes is that the iron blisters, 
becomes " burnt " and very brittle, and cracks. Three years is 
the average life of an iron firebox. The only objection to 
steel is that it sometimes cracks. The average life of the best 
is 9 years and 6 months ; of the worst, 4 years and 4 months; 
of the total reported, 6 years and 4 months. 

The following is considered a good specification for a steel 
locomotive boiler: 

Boiler to be made of mild steel -^-^ inch thick, riveted with 
f-inch rivets placed not over 2\ inches from centre to centre ; 
all horizontal seams and junction of waist and firebox double 
riveted ; all longitudinal seams provided with lap welt, with 
rivets alternating on both sides of main seams, to protect calk- 
ing edges, and all parts well and thoroughly stayed ; top and 
sides of outside firebox all in one sheet ; back-head a perfect 
circle. All plates planed on edges and calked with round- 
pointed calking tools, insuring plates against injury by chipping 
and calking with sharp-edged tools. Boiler tested with 180 lbs. 
to the square inch, steam-pressure. Waist 52 inches in diame- 
ter at smoke-box end, made wagon-top with extended arch with 



DESIGNING STEAM-BOILERS— PROBLEMS IN DESIGN 375 

one dome 30 inches diameter on the wagon-top ; tubes of char- 
coal-iron, No. 12 B, wire-gauge, 200 in number, 2 inches outside 
diameter and 1 1 feet 8f inches in length, with copper ferrules 
on firebox end; firebox made of mild steel, 78 inches long and 
34 inches wide ; all plates thoroughly annealed after flanging ; 
side y^g- and back-sheets f inches thick ; crown-sheet f inches 
thick ; flue-sheet \ inch thick ; water-space 5 inches wide at sides, 
3^ inches wide at back, and 3|- to 4-|- inches wide at front ; 
stay-bolts -§- inch diameter, screwed and riveted to sheets, and 
not over 4J inches from centre to centre ; fire-door opening 
formed by flanging and riveting together the inner and outer 
sheets ; 2 rows of hollow stay-bolts above fire ; 2 rows of telltale 
stay-bolts at top on sides ; crown supported by crown-bars, each 
made of two pieces of 5 X | inches wrought-iron ; placed not 
over 4^ inches between centres, bars to extend across, with ends 
resting on castings on the side-sheets ; crown-bar bolts \ in. 
diameter, with flat heads under the crown-sheet, the fit in the 
crown-sheet to be tapered and drawn to its place by a nut 
above the crown-bar ; the crown to be well and thoroughly 
stayed by braces to dome and outside shell of boiler ; clean- 
ing holes in corner of firebox, and blow-off-cock in side ; smoke- 
stack straight ; grates cast-iron, rocking with dump ; ash-pan 
wrought-iron, dampers front and back ; balanced poppet 
throttle-valve of cast-iron in vertical arm of dry-pipe. 

The firebox first introduced by Mr. Wooten on the Phila- 
delphia and Reading Railway is carried higher than ordinary, so 
as to obtain room for broadening the grate and thus enlarging 
it, so as to be capable of successfully burning the hitherto use- 
less anthracite culm. The dimensions of their common loco- 
motive firebox are 60 and 66 by 32 inches ; the first of new 
design is 8 feet 6 inches long by 7 feet 6i inches wide ; the 
heating-surface of the firebox is 106 square feet, and of the 
combustion-chamber 26 feet, making a total of 982 square feet. 
The grate-rest is between water-bars to prevent burning out, 
and the area is 64 feet. The consumption of coal is only 16 
pounds per hour per square foot of grate-surface against 40 to 
60 pounds in the ordinary locomotive. 

The fuel remains perfectly quiet in the firebox, the consump- 



Zl^ 



THE STEAM-BOILER. 



tion is slow, the steam is more freely made than in the common 
style of locomotive boiler, and no smoke or sparks are ejected 
from the smoke-stack. 




Fig. 



-Stationary " Locomotive" Boiler. 



The stationary boiler of the locomotive type is shown in the 
accompanying figure, as customarily mounted on skids for 
transportation, with gauge-cocks, water-gauge, steam-gauge, and. 
safety-valve attached, and in working order. 



CHAPTER IX. 

DESIGNING ACCESSORIES — SETTING — CHIMNEYS. 

177. The Setting of Boilers which are not self-contained 
involves the construction of a system of side-walls and bridge- 
walls, customarily of brickwork, and entails so great an expense 
as often to make the question of the adoption of the firebox or 




Fig. 80. — Setting of Tubular Boiler. 

the plain boiler one of serious importance. It is usually found 
to be economical to adopt the firebox boiler for small powers, 
and to employ the other type where large quantities of steam 
are to be made. 

The form of the setting, the arrangement of bridge-walls, and 
the number, size, and disposition of flues, are all matters of 
ready determination once the style of boiler is settled ; but 
while the best engineers have come to a nearly uniform and 



37^ 



THE STEAM-BOILER. 



standard design, a great variety of forms and proportions are 
actually in use for every one of the familiar boilers. General 
practice prescribes the use of a cast-iron front protected from 
the action of the fire by a fire-brick lining. Side-walls are of 
red or common brick, lined with fire-brick wherever exposed to 
the direct action of the flame. The bridge-wall adjacent to the 
furnace is of fire-brick, except in parts so located as to be pro- 
tected from the impinging flame ; and the flues, even, are some- 
times similarly lined. The brickwork is held in place and the 
whole structure kept together by tie-rods and binding-bars, of 
which the fastening bolts are so located as to be exposed only 
to moderate temperatures. 

The foUov/ing figure illustrates such a setting for a horizon- 
tal tubular boiler of good proportions : 




Fig. 8i.— Setting of Horizontal Tubular Boiler. 

Here a set of i2-inch-side walls are lined with an inner wall, 
and an air-space between intercepts the heat, and is itself partly 
or wholly of fire-brick. Vertical binders on each side, tied 
together by heavy transverse bolts at top and bottom, hold all 
in place ; and similar bolts tie the front to the rear wall. The 
bridge-wall is set inside, at the rear of the grates, and is raised 
just high enough to prevent fuel falling or being thrown back 
under the boiler. 

The practice of the Hartford Boiler Insurance Co. is illus- 
trated by the next figure, in which are given the dimensions of 
setting for a '' 6o-inch" tubular boiler, as published in the speci- 



DESIGiVING A CCESSOAVJ^:S—SE TTING—CHIMNE YS. 



379 



fication. In this sketch the fire-brick used in hning the walls 
is sharply distinguished from the remainder. 

Where no circulation is permitted there is no objection to 
allowing the spaces above and below the boiler to communicate. 
In some cases the space above the boiler, when closed in, is 
used as a flue, with the effect of drying, and sometimes of 
superheating, the steam. There is an unquestioned advantage 
in keeping the boiler as nearly of uniform temperature as pos- 
sible ; but many engineers consider this system to involve some 
risk. The suspension of the boiler is a matter demanding the 
greatest care. It was formerly the custom to pay little atten- 
tion to this matter ; but the occasional explosion of a boiler in 
consequence of irregular strains so induced, has led to more 




Fig. 82.— Setting of Tubular Boiler, 



careful design. The most common system is probably that in 
which the boiler has a set of cast-iron lugs riveted on its sides 
and resting on plates built into the brickwork of the side-walls, 
thus distributing the weight. In some cases the boiler is sus- 
pended from transverse girders resting, at each end, on the side- 
walls of the setting; and the heads of the supporting bolts have 
sometimes been carried on springs to insure an equalization of 
load and its uniform and safe distribution — which is the essen- 
tial aim of all good systems of support. Where two points of 
support are chosen on each side, they should be placed one 
fourth the length of the boiler from each end ; where three 
supports are introduced, the outer ones should be one sixth 
the length of the boiler from the ends, and the third should be 



380 THE STEAM-BOILER. 

placed in the middle, thus giving a uniform load on all. 
Horizontal boilers are sometimes supported at the rear end on 
plates resting on rollers to reduce frictional resistance to change 
of dimensions. 

It is probably as well not to attempt to carry the weight of 
the boiler on the walls of its setting, and this can be avoided 
by adopting the plan of inserting vertical posts, made of a pair 
of channel-bars secured back to back, and thus forming strong, 
simple, and inexpensive columns, on which the load can be 
safely and permanently carried. The air-space between the 
walls is an important safeguard against injury by the change of 
form of the inner wall with variation of temperature. Where 
desirable, the space between the boiler and this continually 
moving mass can be closed by carrying a flange of angle-iron 
along it, and supporting this flange from the iron posts in the 
walls. Angle and channel irons are also best for use in making 
the binders or " buckstaves" by which the whole setting is 
kept in shape. Where cast-iron is used at all, as in the fronts, 
it should be heavy enough to keep its shape. 

Where a boiler is supported by lugs riveted to its sides and 
bearing on the side-walls of the setting, the principal risk is 
usually, probably, that of the failure of the riveting. The 
boiler-shell has a large margin of strength, and no injury need 
ordinarily be feared from the stress coming of its own weight 
between the points of support. When the rivets are placed not 
more than four or five diameters apart, the boiler may be con- 
sidered as perfectly safe, the workmanship being good. It is 
advisable to place covering strips on the inside to take the 
heads of the rivets securing the lugs in place. 

178. Forms of Covering to prevent the loss of heat from 
the boiler and flues by conduction and radiation are of consid- 
erable variety. The rudest, though an effective one, is a layer 
of ashes over the top of the boiler, filling in between the side- 
walls of the setting. This is often objectionable, as giving rise 
to annoyance from dust ; and various mineral and fibrous sub- 
stances are preferred, such as asbestos, hair-felt, and several 
kinds of plaster and cement. Where hair-felt is used, it is 
often covered with canvas to give a neater appearance, and to 



DESIGNING A CCESSORIES—SE TUNG- CHIMNE VS. 3 8 I 

protect the felt from dust and injury. Occasionally, a brick 
arch is turned over the whole structure, and the air-space so 
produced relied upon to intercept heat. This construction is 
probably not quite as efficient as the other coverings, but it 
has the advantage of permitting easy access to the boiler for 
inspection and repair. 

179. The Form of the Bridge-wall is not always the same 
in the same general design. A bridge-wall is needed at the rear 
end of the grate, and it is now rather unusual to build others ; 
but two, or even more, are sometimes introduced for the 
alleged purpose of securing intermingling of the currents of 
furnace-gas and their contact with the boiler. In some cases 
the bridge-wall is carried up to the boiler-shell nearly, and 
fitted rather closely to its form; a more approved system, how- 
ever, gives its top a perfectly straight and level line. Ample 
space should always be allowed for the passage of the gases, as 
well as above the grates, for the completion of combustion. The 
semi-diameter of the boiler is none too great for the depth of 
this latter space. 

180. The Disposition of Flues is subject to the same re- 
mark as was made relative to the bridge-wall. No standard 
practice can be described ; but it is continually becoming more 
usual to leave the whole space beneath the boiler without 
subdivision from bridge-wall to chimney-flue, taking off the 
gases from the tubes as directly to the chimney as possible, and 
controlling the flow of the gas-current by the damper. Oc- 
casionally a special direct flue is provided with its own dam- 
per, when a drop flue is ordinarily used, or when the flame is 
carried over the shell, the former being opened when the fires 
are started to secure rapid kindling, and closed again when the 
fires are fairly burning. The shortest line of flue from the 
boiler-setting to the chimney is best in all cases. 

181. The Location and Design of Chimney may often be 
the first step to be taken preliminarily to designing the boiler ; 
or, as is oftener the case, the user purchases his boiler and then 
erects such a chimney as the designer and vender may recom- 
mend, in such location as he may find practicable. In many 
cases the chimney consists of a simple pipe of sheet-iron, ris- 



382 THE STEAM-BOILER. 

ing directly from the flue, which, forming part of the boiler set- 
ting, also serves as the base of the pipe. In this case the rules for 
proportioning are to be taken as those governing marine prac- 
tice, and the draught as calculable on that basis, with a consid- 
erable margin to allow for variations of temperature, humidity, 
and mobility of atmosphere. In the majority of cases, how- 
ever, a chimney-stack of brickwork is preferred, both on the 
score of permanence and on that of better draught ; the iron flue 
permitting a loss of heat and cooling of the air-column, which 
does not take place to any observable extent in the brick 
stack. No. 10 or 12 iron is ordinarily used. 

The essentials of a good design are : adaptation in draught 
power and capacity, in height and area of flue, to the precise 
conditions to be met, with ample surplus for emergencies; a 
solid and perfectly safe foundation ; a well-formed, straight, 
well-proportioned shaft ; stability against the pressure of the 
most violent winds ; security against injury by its own heated 
gases ; and economy in construction and maintenance. The 
first two of these requirements are met by the methods already 
detailed in § 160: a safe foundation is obtained by going down 
to the rock wherever possible, or to firm, compact, stable soil', 
and there starting the bed courses, giving them ample area to 
carry the superincumbent weight safely. Where difficulty is 
met with in the endeavor to accomplish this, a broad concrete 
base is often laid on the yielding substratum of soil, and on 
this the masonry is laid up after ample time for hardening and 
settling is allowed. The more slowly the construction is car- 
ried on, the better the result. The form and proportion of the 
shaft is partly a matter of taste, judgment, and architectural 
effect, and partly of calculation based on the elements pre- 
scribed by the conditions under which the boiler is to be oper- 
ated. Stability is assured by carefully proportioning weight 
of stack and breadth at the foundation to meet the overturn- 
ing force of the highest winds, and allowing, further, a fair fac- 
tor of safety. A pressure of 55 pounds per square foot (268 
kgs. per sq. m.) on chimneys of square section, and one half 
this amount on chimneys of circular or octagonal section, is a 
common assumption as a measure of the maximum force of 



DESIGNING ACCESSORIES— SET riNG— CHIMNEYS. 383 

the wind in exposed situations. In sheltered localities, a cal- 
culation of stability is rarely made. Security against the cut- 
ting or overheating which may sometimes occur where the fur- 
nace gases reach the chimney at a very high temperature is 
obtained in large chimneys by the construction of an inner 
chimney of fire-brick, separated from the main structure by a 
narrow air-space. In small chimneys a lining of fire-brick built 
into the walls of the chimney for some distance upward from 
the base is the usual safeguard, and even this is often omitted. 
Economy is obtained by making the design as simple, the 
height and the dimensions generally as small, as may be con- 
sistent with a good design. 

Circular and octagonal sections are best as a rule, but the 
square section is usually the least costly to build. Where an 
outer and an inner shell are put up separately from the foun- 
dation, provision is often made to cover, in some way, the 
annular opening between the two at the top of the inner stack 
to prevent the settlement of dust between them : this is not, 
however, usual or essential ; but a cleaning door should be 
placed at the bottom, through which access can be had both 
to this space and to the main flue. All the talent of the archi- 
tect is often demanded in the design of the exterior of large 
chimneys. 

The following are the dimensions of a large chimney of good 
design :* 

Height above grade 192 ft. 58.5 m. 

Total height (with foundation). . . 204 ft. 62.18 m. 

Batter. ... 2 in 100, nearly. 

Diameter at grade 17 ft. 5.18 m. 

of flue at top 8 ft. 2.43 m. 

Thickness, Slack 2.67 to 1.33 ft. 0.8 to 0.4 m. 

inner shell 1.33 to 0.67 ft. 0.4 to 0.2 m. 

Weight 2,187 tons. 2,222 tonnes. 

Horse-power 2.700. 

Cost per H.-P $5.53- 

" total . $14,000. 

182. Steam and Water Pipes and their connections should 
be as carefully designed and located as the members of the 

* Sci. A?n. Supp.y Jan. 29, 1887. 



384 THE STEAM-BOILER. 

structure itself. Steam should be taken off at the point at 
which it will pass out most perfectly dry, or, if provision is 
made for it, superheated. If a steam-dome is attached to the 
boiler it should usually be placed at a distance from that part 
of the steam-space into which steam is rising most rapidly, and 
the steam-pipe should be led from the highest point within 
it. If a dry pipe is used it is better to so place it that its most 
contracted openings are nearest the furnace. Such area should 
be given this pipe that the frictional resistance to flow should 
not sensibly reduce its pressure, and the same precaution 
should be taken in placing- valves. A velocity of 6000 feet 
(1829 m.) per minute should usually be a maximum rate of flow. 
The steam-pipe should be as carefully protected by non- 
conducting covering as the boiler itself, and it should be so set 
and drained that no water can collect at low points or in an- 
gles, to be thrown forward by the steam into the engine, there 
to cause danger of accident. The Author has frequently known 
this to occur, and the steam-pipe itself is sometimes burst open 
by its impact, causing loss of both life and property. Experi- 
ments conducted by the Author^ have shown that pressures 
produced by this so-called "water-hammer" may amount to 
probably above ten times that which the pipe w^as expected to 
sustain in regular work. Drain-cocks and steam-traps suitably 
placed may be used to take away water collecting in bends 
where they are unavoidably introduced. Care must be taken, 
in long straight lines of pipe, to avoid danger of injury by the 
expansion and contraction taking place with change of temper- 
ature as the pipe is heated and cooled when steam is sent 
through it or when emptied. Where precautions are not taken, 
as in the introduction of bends, angles, or slip-joints or their 
equivalents, pipes are sometimes broken, joints are set leaking, 
or connections are completely broken, and serious results fol- 
low. If extensive systems of pipe are properly guarded against 
water-hammer and excessive temperature-strains by correct lo- 
cation, thorough drainage, and good designing, no other dan- 
ger than that of corrosion is to be apprehended. 



* Trans. Am. Soc. Mec, Engs., vol; iv., 1882-83, P- 404- 



£>ESIG.\'IXG A CCESS0IUES—SE7'TING— CIIIMNE YS. 385 

Similar principles control the location and proportioning of 
feed-water pipes. They should be of ample size and strength, 
should be so located as to be free from liability to injury by 
expansion and contraction, and should be led into the boiler in 
such manner and should so discharge the feed-water that in- 
jury should not be done the boiler by the impinging of cold 
water on heating-surfaces, or by the collection of a mass of cold 
water at times in the lower part of the boiler, thus introducing 
serious strains, along the line separating the cold from the hot 
water, or elsewhere. The entering feed should be warmed by 
flowing out into the general mass of circulating liquid, and 
should not be so directed as to impinge on metal. No calcu- 
lations of strength of ordinary steam and water pipe are ordi- 
narily made, as the internal pressure is usually the least impor- 
tant stress affecting them. If strong enough to bear other 
stresses and thick enough to resist corrosion for a considerable 
time, they are amply strong. 

All cocks, valves, and connections should be strong enough 
and sufficiently well put together to bear safely such accidental 
stresses as have been referred to without risk. 

183. Safety-valves are absolutely essential to every steam- 
boiler. Many explosions have been known to have been caused 
by the failure of a safety-valve to open at the intended pres- 
sure, and it is considered good practice to evade such a danger 
by introducing two safety-valves into the design of every 
boiler. 

The office of a safety-valve, as used on a steam-boiler, is to- 
discharge steam so rapidly, when the pressure within the boiler 
reaches a fixed limit, that no important increase of pressure can 
then occur, however rapidly steam may be made. It has also 
another office : it should be so constructed and arranged that 
should any accident occur it may be opened by hand and the 
steam-pressure lowered very rapidly, even when the fires in the 
boilers are burning brightly and generating steam with maxi- 
mum rapidity. The size of a safety-valve is determined by the 
character of the valve itself, by the pressure at which the steam 
is to be discharged, by the difference permissible between the 
pressure at which the valve is to open automatically, and that 



386 THE STEAM-BOILER. 

at which it is intended to be capable of discharging steam as 
fast as the boiler can make it. 

A valve of defective design or badly constructed must nec- 
essarily be larger, to do the same work, than one of similar 
type well designed and constructed. Steam is discharged at 
any given rate through an orifice of smaller dimensions as the 
pressure increases ; the lower the pressure, on the other hand, 
the larger must be the valve. A boiler in w^hich steam is car- 
ried at ordinary pressure may require a safety-valve of large 
area, while the same quantity of steam would escape through a 
rivet-hole in a boiler containing steam at pressures sruch as 
were attained by Perkins and Albans a generation ago. 

Rules by which to calculate the proper area of safety-valves 
for every case arising in his practice are used by every engineer 
accustomed to designing steam-boilers. These rules vary con- 
siderably with differences in the experience or the judgment 
of their authors. 

But a safety-valve, as has been stated, should be capable of 
discharging very much more than the maximum quantity of 
steam that the boiler can make when doing its best. The 
valve must be raised, ordinarily, by the action of the steam it- 
self, and the force exerted by the steam-pressure upon its disk 
rapidly diminishes as it rises from its seat. The seat is bev- 
elled, too, in such a manner that the effective area for dis- 
charge of steam is but a fraction of that due the rise of a valve 
having an unbevelled seat. It is therefore advisable to give a 
very large area to the valves. 

It has been common in the United States to allow but 
one square inch of area of valve-opening for 25 square feet of 
heating-surface, or a ratio of 0.0003, nearly ; while another rule 
gives one square inch to three feet of grate-surface : an English 
rule allows an area equal to a half square inch to a square foot 
of grate, or 0.003 the grate-surface, nearly ; while still another 
authority nearly doubles this area of valve. But the area 
should always be based on the quantity of steam made. The 
Author has been led by experience to adopt the rule : Multiply 
the maximum weight of steam which the boiler is expected to 
generate per hour by five and divide by ten times the gauge- 



DESIGNING A CCESSORIES—SE TTING— CHIMNE Y S. 38^ 

pressure, increased by ten, in British measures ; or, divide that 
weight by twice the latter quantity. Thus, 



0.5W 
a— , -" ; 
/ + 10 



where w is the maximum weight of steam made per hour in 
pounds, / the pressure in pounds on the square inch, and a the 
area of the valve-opening in square inches. 

For important work it is advisable, especially for large 
boilers, to calculate carefully the area of opening needed, by 
the principles controlling the discharge of steam from orifices. 
A very large excess over the area demanded to just discharge 
steam at the maximum rate at which it is made should be 
given, as it is often necessary to rapidly reduce pressure just 
when the fires are brightest and vaporization most active. 
The design of the valve is rarely a problem solved by the de- 
signer of the boiler. Valves in great variety are made and 
sold by manufacturers, and it is customary to purchase such 
as are needed. 

One of the simplest of the common form, of lever safety- 
valve is that seen in Fig. 83, in 
which the valve, A, is held down 
to its seat by a lever, BC, having 
a fulcrum at the pin, (7, and resting 
on the valve at D. The weight, 
W, can be adjusted at any distance 

from D that may give the mo- Fig. 83.— Lever Safety-valve. 

ment required to resist the intended steam-pressure. A guide 
at E^ secured, like the pivot standard F, to the valve-chamber, 
(7, keeps the lever in the designed vertical plane. The size of 
the valve is usually reckoned as that of the opening, //, of 
pipe and valve-seat. A '' feather" on the outer side of the 
valve guides it and ensures its return fairly upon its seat when 
it falls with reduction of pressure. Fig. 84 shows the exterior 
of a better and more recent type of lever safety-valve. In 
some cases weights are carried directly on the top of the valve- 




388 



THE STEAM-BOILER 



stem, a spindle rising from the latter over which they are 
threaded ; the pressure is then determined by adding or re- 
moving weights. In other instances the weights are suspended 
below the valve and inside the boiler, the idea being to make 




Fig. 84.— Safety-valve. 

them inaccessible to any one, except at times when no steam is 
on and when the inspector may adjust them. Often valves are 
so constructed that, once adjusted, they may be locked up, and 
thus made safe against the tampering of irresponsible or mali- 
cious persons. 



-f^* TO POINT OF SUSPENSION OF WEIGHT 




Fig. 85. — Recent Type of Lever Safety-valve with Knife-edges. 



A better form of lever safety-valve than that just described 
is that proposed by the U. S. inspectors, Fig. 85, in which 
the contacts of valve and fulcrum with the lever are made by 
knife-edges, a system found to have marked superiority over 



DESIGNING A CCESSORIES—SE TTING—CHIMNE YS. 389 

the usual pin-construction. The valve is commonly covered 
by a "bonnet," and the steam flowing past the valve into the 
chamber so made is conducted away by an attached steam- 
pipe. 

The proportions adopted by the Board submitting if^ are 
as follows: 



Area of Valves expressed 
IN Square Inches. 


5". 


10". 


15". 


30". 


25". 


30". 


Diameter of opening... 
Diameter of valves. . . . 

Length of lever. 

Distance of fulcrum. .. 
Angle of valve's face. . 

Width of face 

Length of fulcrum link. 


2^525 
2.76 

25. 

'■\, 

•15 

4^5 


3^37 
3 77 
30 • 

•15 

4-5 


4-371 

4.58 
35- 
3-5 
45° 
.12 

4-5 


5^047 
5.28 
40. 
A- 

45'' 
.17 

4-5 


5.642 
5-S6 
45- 
4-5 
45° 
•17 
4-5 


6.781 
6.375 
47-5 
4^75 
45" 
•15 
4.5 



When well proportioned and well made, these valves may 
be expected to keep the steam under usual conditions within 




Fig. 



-Lever Safety-valve (U. S. Board of Inspectors). 



one or two per cent of its working pressure ; but the smaller 
valves are less exact than the larger sizes. 



Report on Safety-valve Test. Washington, 1877. 



390 



THE STEAM-BOILER. 



The essential requirements are considered to be — 
(i) Capability of discharging any excess of steam above a 
fixed working pressure. 

(2) A minimum limit of variation of pressure within which 
the valve will open and close. 

(3) Uniformity of action at different pressures. 

(4) Reliability of action under continued use. 

(5) Simplicity. 

The form of valve just described meets these demands in a 
very satisfactory manner. The working drawings are seen in 
Fig. 86. 

The effective area of opening, (^, required to discharge a 
given weight of steam, w, per hour was found to be, at various 
usual pressures, as follows : 



2 atmos. , 30 pounds per square inch a = w X 0.0009 

4 atmos., 60 pounds per square inch. a = w X 0.0006 

6 atmos., 90 pounds per square inch .a = w X 0.0003 

7 atmos. , 100 pounds per square inch .a = w X 0.0002 



The proportion a = o.oo$w is' taken as giving a safe area, 
the factor of safety for the usual pressures being 10, and greater 
as the pressures increase. 

In many cases the lever and weight are too cumber- 
some, or otherwise objectionable, and a spring is used, acting 
either directly on the valve or on a short lever — a common 
practice with both locomotive and marine boilers. Nearly 
all the later forms of valve are of the former of these two 
classes. 

It is found very difificult to avoid a considerable variation of 
steam-pressure with the common form of valve, as it is not 
often practicable to secure the full lift of the valve. Owing to 
a peculiar action of the impinging currents of steam, it is rarely 
possible to obtain a rise of more than about 0.2 inch (0.5 cm.) 
without serious excess of pressure, especially with low steam. 
Many expedients have been proposed to meet this difficulty, 
as, for example, in the Rochow valve of Fig. 87, in which a 



DESIGN I KG A CCESSORIES—SE TTING— CHIMNE YS. 39 1 




piston is attached below the valve, having a slight excess of 
area, and thus continually forcing the valve upward to the 
limit of its rise until the pressure is relieved. 

A system now becoming very 
common, and giving most satisfac- 
tory results, is that known as the 
" reactionary" valve, of which a 
good example is that of Ashcroft 
(Fig. 88), in which the current issu- 
ing from under the valve is de- 
fleeted by a curved lip or flange 
in such manner as to cause a 
pressure by its reaction that aids 
effectively in raising the valve. 
This system of construction is in 
very extended use. 

When well designed, they open ^^^- 87-RocHow's Safety-valve. 
promptly and widely, discharge the surplus steam quickly, and 
seat themselves at once, thus preventing any observable varia- 
tion of working pressure. 

In designing safety-valves care is 
to be taken to secure ample area of 
opening, freedom from liability to 
stick or failure to rise fully, and to see 
that if the spindle passes through a 
guide the bearing-surfaces are not 
liable to rust fast. It is usual to line 
the opening, and to cover the spindle 
with brass. Narrow valve-seats are 
advisable to secure tightness and 
free working, and straight steam- 
Avays. 

The mechanism of one of the 
most recent of the '' reactionary" safe- 
89, in which B B is a. nickel seat, C C, 
the valve of which, CC, is the adjustable ring introduced to 
secure the desired reaction. FF is the spring and Z>Z> the 




Fig. 88.— Ashcroft s (Reactionary) 
Spring-loaded Safety-yalye. 

tv-valves is seen in Fie- 



392 



THE STEAM-BOILER. 



spindle, 
and the 



the one bearing against the fixed cross-bar, G G, 
other attached to it firmly. The channel, a a, turns 
the issuing current back into the verti- 
cal direction, and thus makes the re- 
actionary effect a maximum. 

Brass or nickel valves and seats are 
free from the liability to dangerous 
corrosion that characterizes iron. 

The maximum intensity of pressure 
under any lever safety-valve is 

p_'wl -^ I'w' -\- w"f 




/« 



Fig. 89.— Richardson's Safety- 
valve. 



when a is its effective area ; iv, w\ w\ 
the weight applied, that of the lever and that of valve ; / /', the 
lengths of lever-arm from weight to fulcrum, and of that from 
centre of gravity of the lever; and /the distance from fulcrum 
to centre of valve. The actual value of a may vary enormously 
in any one valve having a wide seat, accordingly as it is tight 
or leaking. If perfectly tight, the valve will rise when an 
equilibrium is reached, assuming a to be the area within the 
inner periphery of the seat ; it will drop when the pressure has 
fallen so far that an equilibrium may be established, a being 
measured to the exterior periphery. If leaking, these two 
areas may have almost any apparent relation. The narrower 
the seat, the less these differences. 

For large boilers, " multiplex" valves, consisting of a set of 
two or more in one casing, are often used in preference to a 
single large valve. 

184. The Feed Apparatus for steam-boilers is not usually 
designed by the engineer furnishing the plans for boilers, but is 
purchased of makers of feed-pumps or of " injectors" as it may 
be needed. Where open heaters are used, in which the feed is 
heated before it is pumped, the injector cannot, as a rule, be 
used ; but a large slow-moving pump, placed sufficiently low to 
fill with certainty at every stroke, should be employed. A 



DESIGNING A CCESSORIES— SE TTING—CHIMNE YS. 393 

pump driven by belt and by the main engine is more economi- 
cal in operation than a steam-pump. The independence of the 
latter, and their convenience of operation, have caused their 
very general introduction ; and they are commonly kept at 
hand for emergencies, even where the "power-pump" is used. 
With a closed or coil heater water may be forced by the feed- 
pump through the heating-coils and on into the boiler. In 
this case, either pump or injector may be used. The latter is, 
in this case the more economical, as no loss occurs except of 
heat from the steam and water pipes, and this loss may be ren- 
dered insignificant by carefully covering them. Even the 
-effect of friction is to give a fully compensating increase of 
temperature to the water. 

The steam-pumps are not usually economical of steam, and 
often use ten times as much per unit of work done as good 
engines. A " duty" of ten millions is unusually large. 

All feed apparatus should be of the best possible construc- 
tion ; should, when possible, be in duplicate, and of far greater 
capacity than is demanded in regular work ; and should be 
placed where it will always be promptly and readily accessible, 
and kept in perfect order. Failure to act promptly and effec- 
tively in an emergency may lead to incalculable disaster. In 
many cases injectors are used in ordinary work, and very large 
steam-pumps kept in readiness for emergencies. 

Heating the feed-water by means of the waste gases is al- 
ways advisable if at all practicable, as well as the utilization of 
the heat of all exhaust-steam from engines and pumps and re- 
turns from systems of heating-pipe. 

The table on page 394 gives the percentage of saving ef- 
fected by heating the feed-water of a steam-boiler by means 
of heat otherwise wasted. 

185. Minor Accessories and details, such as the kind and 
location of steam and water gauges, dampers, automatic con- 
trolling devices, etc., should be as carefully considered by the 
designer of the steam-boiler as any other parts of his work. 

TJie Steam-gauge is selected from among the numerous 
styles and makes in the market, and is never designed by the 
engineer preparing plans of boilers. The most common form 



394 



THE STEAM-BOILER. 



is the Bourdon Spring Pressure-gauge (Fig. 90), of which a 
number of modifications are in use. The case, A A, encloses 
a coil of flattened tube, B B, closed at the 
free end and open to boiler-steam at the 
supported extremity. As the pressure rises 
and falls, a tendency to expand the tube 
into circular section produces greater or less 
effect, and the tube, as a whole, assumes a 
greater or a smaller radius of curvature, 
throwing its free end one way or the other 
in such manner as to measure, by the trav- 
erse of the attached pointer, the pressure at 
each moment, of the confined fluid. Some- 
held at its middle point, both ends being 
free, and their relative motion affecting the pointer. The 
more stable the tube and the more reliable the mechanism 
connecting it with the hand at the dial, the better the gauge. 




Fig. 90.— Bourdon Gauge 

times the tube 



IS 



SAVING BY HEATING FEED-WATER. 

(Steam at 60 lbs.) 



i 

3 


Initial Temperature of Water (Fahr.). 




"^S-^ 






E^&i 






























32° 


40° 


50° 


60° 


70" 


80° 


go" 


100° 


I20« 


140° 


160° 


180° 


200* 


60° 


2-39 


1. 71 


0.86 























80 


4.09 


3-43 


2.59 


1.74 


88 



















100 


5-79 


5-14 


4-32 


3-49 


2.64 


1.77 


0.90 















120 


7-50 


6.85 


6 


05 


5-23 


4.40 


3-55 


2 


68 


1.80 













140 


9.20 


8-57 


7 


77 


6.97 


6.15 


5-32 


4 


47 


3 


61 


1.84 











160 


10.90 


10 28 





50 


8.72 


7. 91 


7.09 


6 


25 


5 


42 


3-67 


1.87 









180 


12.60 


12.00 


II 


23 


10 46 


9.68 


8.87 


8 


06 


7 


23 


5 52 


3-75 


I 91 







200 


14.30 


-3-71 


13 


00 


12.20 


11-43 


10.65 


9 


B5 


9 


03 


7-.36 


5-62 


3-82 


1.96 





220 


16.00 


15.42 


14 


70 


14.00 


13-19 


12.33 


II 


04 


10 


84 


9.20 


7-50 


5-73 


3-93 


1.98 


240 


17.79 


17-1.3 


16 


42 


15 69 


14.96 


14.20 


13 


43 


12 


65 


"■$5 


9-37 


7.64 


5-90 


3 97 


260 


19.40 


18.85 


18 


IS 


17-44 


16.71 


^5-97 


15 


22 


14 


45 


11.88 


11.24 


9-56 


7.8b 


s-gb 


280 


21 .10 


20.56 


19 


87 


19.18 


18.47 


17-75 


17 


01 


16 


26 


14.72 


13.02 


.1.46 


9-73 


7-94 


300 


22.88 


22.27 


21 61 


20.92 


20 23 


19-52 


18 81 


18.07 


16.49 


14.99 


13-37 


11.70 


9-93 


Fig. 91 represents a section of the Bourdon 


tube. The 


major axis is placed vertically to the plane of the 


coil. Were 


it placed parallel to that plane, internal pressure 




^ 


^zrr^ 



would close up the coil instead of, as in the usual ig. 91. 

case, uncoiling it. This latter is the disposition adopted by 
the Author, as in Fig. 92, in a gauge devised by him for very 



■ DESIGNING ACCESSORIES— SETTING— CHIMNEYS. 395 

high pressures, and especially to work steadily where exposed to 
heavy jar, as on locomotives. 

A pair of corrugated disks, secured together at the edges, 
and receiving steam-pressure within, is a form of pressure-gauge 
spring which has been found useful, and many gauges are thus 
constructed. All spring gauges, unless constructed with ex- 
traordinary care, are very liable to give after a time misleading 
indications, and they should be occasionally tested to ascertain 
to what pressures the readings on the dial actually correspond. 



Fig. 84 

THURSTON'S HIGH-PRESSURE GAUGE 



Fig. 92. — Thurston's High-pressure Gauge. 




Mercury-gauges, in which the pressure is measured by the 
height of a mercury column balancing it, are much safer than 
spring-gauges, but are too cumbersome for common use. All 
other steam-gauges are, however, referred to the mercury-gauge 
in standardizing them. 



39^ 



THE STEAM-BOILER. 



Steam-gauge connections should be so made that the in- 
strument may not be Hable to injury by heat, either externally 
or internally, and so that the spring shall always have a body 
of comparatively cold water interposed between itself and the 
steam. A coil or siphon-shaped bend in the gauge-pipe is gen- 
erally introduced with this purpose in view : it fills up with a 
body of water condensed from the steam which protects the 
spring from injury by exposure to heat. The point of entrance 
of the gauge-pipe into the boiler is simply a matter of conven- 
ience, usually. 

Gauge-cocks and water-gauges should be set where they will 
not be affected by any foaming that may occur within the 
boiler; they should be as far from the furnace as is conven- 
ient, or their connections should be led to a quiet part of the 
boiler. A foaming boiler, by deceiving the eye at the gauges, 
may discharge a dangerously large amount of water undetected. 
TJie Low-water Detector and Alarm is an apparatus which is 
in very common use to give warning should the water-level 
ever fall below that considered safe. It com- 
monly consists of a vertical tube closed at the 
top by a fusible plug, or by a valve actuated 
by a rod having a different coefficient of ex- 
pansion from the tube itself. The tube com- 
municates at the lower end with the water- 
space of the boiler. It ordinarily stands full of 
water; but should the water-level fall below 
its lower end, steam displaces the water in the 
tube, the fusible plug melts, or the valve is 
opened by the difference in expansion of the 
tube and rod, and steam at once issues, giving warning of dan- 
ger. The upper end of the tube is commonly fitted with a 
steam-whistle, the blowing of which when the steam makes its 
exit insures attention. 

Many forms of grate-bars are used in steam-boiler furnaces, 
some of which are provided with interlocking devices so con- 
trived that all are so bound together that it is impossible for 
single bars to warp and twist out of shape to such an extent 
that they will be liable to burn. In other cases the bars are 
fitted so as to be all capable of vibration or rotation by the ac- 




FiG. 93. — Low-water 
Alarm. 



DESIGNING A CCESSQRIES—SE TTING—CHIMNE YS. 39/ 

tion of a single handle, and thus to permit convenient cleaning 
of the fires. Such grates are in very common use in anthracite- 
burning furnaces. 

Fusible plugs are inserted at convenient points in plates lia- 
ble to be the first to be left dry on the falling of the water- 
level. A leaden rivet in an upper seam or in a rivet-hole 
made for the purpose at the highest part of a crown-sheet is 
often relied upon ; but it is better to use an alloy of lower 
melting-point, and to make it quite large. Several small plugs 
are sometimes inserted in a larger plug of cast-iron properly 
located, the idea being to thus secure greater safety by avoid- 
ing the chance of a single one failing to serve its purpose. A 
large plug of fusible metal, projecting well above the crown- 
sheet or other plate in which it may be placed, and having a 
central rod of copper passing completely through it and pro- 
jecting at top and bottom, is a very excellent device. When 
its upper end becomes exposed the copper rod melts out of its 
casing and falls down out of the way, exposing clean surfaces of 
fusible metal, which in turn melt, and the purpose of the appa- 
ratus is accomplished with certainty. In some cases alloys are 
so altered by long exposure to heat that they fail to melt when 
the emergency arises. It is advised by the best engineers that 
they be renewed frequently. An accumulation of sediment or 
scale sometimes prevents their working, or may permit their 
melting without causing egress of steam and water, as is usu- 
ally intended. A coating of thin scale will often sustain all 
the pressure coming upon it over such an opening as is left by 
the dropping out of the plug. 

The best fusible plugs consist, as a rule, of an outer shell, 
as in the figure, filled with a fusible metal, C, in the form of a 
plug extending through the shell from top 
to bottom. The shell should be of hard 
brass to insure strength, with a good thread 
where it screws into the plate, and a good 
hexagonal or square head, and durability suf- 
ficient to permit several fillings. The thread 
cut in the shell should correspond with the 
gas-fitters' standard. The use of such plugs fig. 44.-fusible Plug. 
is often required by law. 




398 



THE STEAM-BOJLER. 



Low temperatures can be determined by the melting-points 
of compositions of lead, tin, and bismuth ; and the following 
may be used for fusible plugs:* 



An alloy of i part lead, i part tin, 4 parts bismuth, melts at 94° C 



Rose's metal 



94' 

100 

100 

118.9 

141. 2 

241 

167.7 

167.7 

200 



201° F. 
202 
202 
246 

257 
466 

334 
334 
392 



It is customary to use such compositions in making '' fusi- 
ble plugs" to be inserted in the crown-sheets or tops of '^ con- 
nections" liable to be injured by low water, to %\mq warning of 
danger, and to act as safety devices by melting when uncovered 
and permitting steam to issue into the furnace and flues. 

All marine boilers subject to the rules of the United States 
Treasury Department are required to have plugs of Banca tin 
inserted, of not less than 0.5 diameter in the smallest part.f 
Cylinder boilers with flues must have one in each flue, and one 
in the shell not less than four feet from the forward end. Fire- 
box boilers must have a plug in the crown-sheet. Upright tu- 
bular boilers must have a plug in one of the tubes, two inches 
or more below the lower gauge-cock, or in the upper tube- 
sheet if so preferred by the inspector. 

Where manhole covers can be '' struck up" in wrought-iron, 
as many of them are now often made, they 
are much safer, as well as lighter and more 
convenient of manipulation. The accom- 
panying figure illustrates such a construc- 
tion as introduced some years ago. The 
two guards and bolts give greatly increased 
security as compared with the ordinary ar- 
rangement of a single guard and bolt at the 
middle of the cover. 

The M'Neil manhole cover and guard 
represent good recent practice, as seen 
in Fig. 96. The opening through the shell 




Fig. 95. — Wrought-iron 
Manhole Plate. 



Weisbach. 



f Regulations, § 22. 



DESIGNING A CCESSORIES— SE T TING— CHIMNE YS. 399 

is strengthened by a wrought-iron " struck-up" ring, the 
section of which is L-shaped. The inner edge is faced to re- 
ceive the faced bearing-surface of the cover, and thus makes a 
steam-tight joint without requiring packing. 




Fig. 96.— M'Neil Manhole Cover. 

The " blow-off cock," which controls the discharge of water 
through the " blow-off " pipe, should never have a valve substi- 
tuted for it, but only a good conical cock should be used. It 
should be of the best of brass or bronze, and of extra strength. 
A valve is liable to be caused to leak by the catching of dirt 
or of chips between it and its seat, and thus to endanger the 
boiler by undetected leakage. With the cock no uncertainty 
can exist in regard to its being open or closed, and foreign 
matter caught by the plug will be cut off, or the cock will be 
opened an instant to wash it away. A " T " placed outside the 
cock and so arranged that the plug can be taken out to see 
Avhether the blow-cock leaks, and if so how much, will be 
found an important element of security. 

The " feed-valve" which controls the introduction of the 
feed-water into the boiler should always be a strong, well-made 
brass valve, of the best of metal and heavier than the customary 
market valves. The ordinary steam-fitter's valve and other 
brass-work is usually much too light, and it is often thought 
wise to make special patterns for boiler connections. The 
valve should be placed close to the boiler and the check-valve 
outside, and as near it as possible. Often a single valve — 
a '' screw-check" — serves both purposes. It should be so 
placed that in case of the valve getting loose it may not pre- 
vent the entrance of the water into the boiler. 



CHAPTER X. 

COXSTRUCTIOX OF STEAM-BOILERS. 

i86. The Methods and Processes employed in the shop 
in the construction of steam-boilers are usually simple, and in- 
capable of very great refinement. The boiler-maker receives a 
set of drawings from the designing engineer, which exhibit 
the general form and proportions of the boiler, and complete 
representations of all details. 

These drawings should include front and side elevations^ 
and plan, together with sections taken wherever necessary to 
exhibit the internal arrangement and structure. All dimen- 
sions should be carefully marked on each sheet, and the work- 
men instructed to *'go by the figures," as attempts to measure 
by scale are apt to lead to mistakes. The thickness of each 
sheet should be indicated, and the location, form, and size of 
every opening to be made in the shop. General plans are 
commonly made on a scale of from ^^ to ^ full size, ac- 
cording to circumstances ; but detail drawings are often all 
made full size. 

The boiler-maker often reproduces the general drawings, as 
well as all details, full size, on a set of large boards provided 
for the purpose, and, measuring all parts anew, makes sure 
that the originally given dimensions are all right and consis- 
tent with each other. The location of each sheet and its 
seams being thus determinable, the dimensions of the rectangu- 
lar, or other simple form, of sheet, as it is to come from the 
mill, are ascertained, and if not in stock, the iron or steel is 
ordered. Mills will usually be able to supply sheets cut very 
exactly to the ultimate size and shape, and thus save great 
expense in cutting and fitting in the shop. Every sheet should 
be ordered as exactly as to size as possible, and the grade 
and quality should be as precisely specified in the order-list 
thus made. 



* 



CONSTRUCTION OF STEAM-BOILERS. 4OI 

All special sheets should be exhibited by sketches as well 
as by figures, and in arranging their location and dimensions 
care is taken to bring just as few seams into the furnace and 
to expose riveting to the heated gases as little as possible ; 
heavy laps, two, three, or even more sheets coming together 
in the joint, as is sometimes the case, are very apt to make 
trouble. Laps should be so planned, also, as to be easily 
reached for chipping and calking when necessary. The larger 
the sheets, generally, the better. 

The order being filled, the work of construction is begun, 

187. The Apparatus, Tools, and Machinery employed 
in boiler-making are of the simplest character ; although the 
tendency is constantly observed to introduce more machine- 
work to the exclusion of hand-work, and to make steam-boiler 
construction, like iron-bridge construction, approximate more 
and more to the art of the machinist. The boiler-maker is 
coming to work more and more to gauges and standards, and 
the boiler is getting to be more and more a machine-made 
product. 

The apparatus used in taking off the dimensions from the 
working drawings and laying them down on the sheet consists 
of a set of rules, scales, straight-edges, and templates. The 
latter are usually strips or frames, which may be laid down on 
the sheet, and which contain carefully spaced holes correspond- 
ing to the rivet-holes to be made, in number, size, and loca- 
tion ; they permit the location of the rivet-holes with accuracy 
and dispatch. 

The tools employed in boiler-making consist of tongs with 
which to handle hot rivets ; riveting-hammers, especially de- 
signed for their work ; chipping chisels for use in trimming the 
edges of plates ; cape-chisels with narrow cutting edges for 
cutting off portions of the sheet, or making openings in it ; 
and hammers for driving these chisels. Drift-pins— tapering 
iron pins which are inserted in the rivet-holes to draw them 
into line — are also used, sometimes endangering the construc- 
tion ; calking tools are used for making seams tight, and 
" expanders" to " set" tubes. 

The macJiincry of the boiler-maker consists of heavy rolls 
26 



402 THE STEAM-BOILER. 

for giving the sheets the cylindrical form ; shears for cutting 
them to correct outline ; punches for making rivet-holes ; 
boring-lathes or drill-presses for making the large holes in tube 
or flue sheets ; and riveting-machines. Where large boilers, to 
carry high pressure, and therefore made of heavy plates, are 
to be built, all these tools must be very heavy and powerful. 
Reamers, or '' rimmers," are used to enlarge holes found to be 
too small for their purpose. In the best-equipped establish- 
ments a planer is used to give the edges of heavy plates their 
bevel, and that exactness of line that is essential to neatness of 
appearance along the lap, as well as to secure immunity from 
injury by the chisel when the edge of the lap is chipped in the 
older way, preparatory to calking. 

Various kinds of rivet-heating furnaces complete this list 
of apparatus of the boiler-shop. All such machinery should be 
very substantial and powerful, as it is always liable to be sub- 
jected to very heavy stresses. 

i88. Shearing, Planing, and Shaping the sheets to the 
prescribed size and form are operations preliminary to the 
fitting together and riveting up of the work. 

Shearing is performed by the '' shears" or shearing-machine, 
which consists of a pair of strong jaws, of which the one is 
fixed, the other movable, and actuated by a powerful toggle- 
joint or by an eccentric. The cutting edges are usually 
straight, but set at a slight inclination the one with the other, 
in such manner that the cut begins at one end of the blade 
and runs across to the other, thus enormously reducing the 
force required to effect it. This operation is rapid and inex- 
pensive, but is liable to injure the metal near the cut if it is 
hard, and usually leaves so rough an edge that it is advisable 
to give a better finish by means of the planer. Sharply curved 
and irregular outlines cannot be given by the shears or the 
planer, and are formed by the chisel. Occasionally, the rough 
work is done by drilling a series of holes along the line to be 
cut, and dressing out to the line with the chisel. 

189. Flanging sheets which are to receive the ends of 
flues, or are to be used as heads and riveted to the shell, is 
performed at open fires, by means of which an even heat is ob- 



CONSTRUCTION OF STEAM-BOILERS. 403 

tained over the whole area to be worked, and the flange is then 
made by hammering the edge to be turned, over an anvil or 
properly shaped '' former." In some cases, when considerable 
num-bers of circular or other simple forms are to be flanged, 
flanging-machines are used, in which the whole flange is formed 
at one operation, the disk being forced by hydraulic pressure 
into a die which turns up the flange all around. In some 
cases dome-tops, manhole-rings, manhole-plates, and other 
parts are similarly " struck up." 

Punching and drilling are performed by machinery usually, 
and for the latter process the gang-drill is often found an 
economical machine : it consists of a collection of drills so set 
as to be driven together, and so to make a number of holes 
at once. Punching is generally practised with very soft steels, 
and with all iron ; but drilling is always preferable where steel 
is employed of appreciably greater hardness than good iron, 
and is probably safest with hard irons. 

A good rule in working steel plate is to punch the holes 
-f^ inch (0.476 cm.) smaller than the size of rivet, and then to 
enlarge the hole to full size by either counterboring or ream- 
ing. The sharp edge, or fin, if any, around the hole should 
finally be trimmed so as to make a slightly rounded fillet under 
the head of the rivet, and thus reduce the risk of fracture at 
that point. 

For these operations the holes have been previously marked 
off by the template, and the art of successfully doing the work 
is mainly that of securing exact location of the punch or drill 
at starting. A table, carrying the plate and moving automati- 
cally the correct distance to give the desired spacing at each 
operation, is often adopted, and with advantage. When punch- 
ing, the sheet should be so placed that the side at which the 
punch enters shall be that next the adjacent sheet when 
riveted up, thus producing a hole for the rivet largest on the 
outside, next the heads, and smallest at the middle. 

190. Bending Plates to the required curvature is often 
the first process, though frequently performed after the opera- 
tions just described are completed. The bending rolls are so 
set as to produce a moderate degree of curvature at the first 



404 THE STEAM-BOILER. 

passage of the plate, and repeatedly adjusting the rolls and 
successive passes of the sheet finally give the full curvature 
desired. Where the shape to be secured is the frustum of a 
cone, one end of the sheet is more closely pressed in the rolls 
than the other, and a sharper curvature given it. The use of 
a template determines when the plate has the right curvature. 

191. Riveting is done partly on detached portions of the 
boiler, as in making flues and fireboxes, and partly in assem- 
bling such parts and building up the complete structure. As 
a rule, all parts which can be easily handled are completed 
separately, and later joined to adjacent parts in the final work 
of putting them all together. Each member being compara- 
tively light and small, the work can be done on it, detached, 
much more conveniently, rapidly, and cheaply than when it is 
attempted to construct it as an attached portion of the larger 
mass. 

Before riveting up, each scam is examined to see that the 
two halves of the lap are precisely matched, the edges parallel 
and well adjusted, and opposite rivet-holes all exactly located 
and fair with each other. Should any fault appear it is cor- 
rected before riveting is begun. While making this trial of 
parts and doing this fitting, and while making this examina- 
tion, the seam is temporarily held by bolts which should nearly 
fit the holes intended for the rivets. Should a pair of rivet- 
holes be unfair, the bolt will not enter, and one or both the 
holes must be dressed over with a reamer until the rivet can 
enter. The drift-pin is used to bring companion sets of holes 
opposite, when in doing this the plate requires to be slightly 
sprung ; but it ought never to be employed to enlarge the 
holes or to force them fair by visibly distorting the sheet or 
the metal about the hole. When this process seems necessary, 
and when enlargement by chipping produces a seriously mis- 
shapen hole, the faulty sheet, or pair of sheets, should both be 
in fault, should be condemned, and better prepared sheets 
substituted. 

When the seam is found to be right, the two edges are 
bolted firmly in position, with the laps in perfect contact, and 
riveting proceeded with. Every rivet should be of the length 



CONSTRUCTION OF STEAM-BOILERS. 



405 



and size required by specification, and of the best material. In 
heating, the shank is given a good forging temperature, the 
head left barely red, and the point safely inside the burning 
heat. A few blows on the laps, with the rivet in place, deter- 
mine whether metallic contact exists, and the rivet is then 
rapidly headed up and shaped. Quick work means easy and 
good work, as the riveting is then finished before the rivet is 
hardened by cooling. Riveting-hammers are comparatively 
light ; but the rivet is held up to its place by heavy hammers, 




Fig. 97.— Steam Riveting-machine. 



weighing from ten to sometimes thirty or forty pounds (4.5 to 
14 or 18 kgs.), and capable by their inertia of resisting the 
heaviest blows struck during the operation. Two or three 
hundred blows are required for each rivet in ordinary boiler- 
work. Very heavy rivets are headed up with a *' button-set," 
a forming tool which is cup-shaped at one end, where it rests 
on the point of the rivet, while blows of a sledge-hammer 
on its other end drive it down and so give the head a hemi- 
spherical shape. This form of head is stronger than the cone- 
shape usually given in hand-riveting. 



4o6 



THE STEAM-BOILER. 



Machine-riveting, either by steam, compressed air, or hy- 
drauHc machines, is, if well done, preferred to any hand-rivet- 
ing ; although on work which is not too heavy the latter is 
thoroughly capable of giving satisfaction. In machine-riveting 
the machine should be amply powerful ; the die should be 
carefully brought in line with the rivet ; the laps should be 
very closely secured together, and the pressure fully up to the 
working standard. A machine which will clamp and hold the 
lap while the rivet is driven is to be preferred. 




Fig. 



-Hydraulic Riveter. 



Well-constructed steam-riveters of angular size do their work 
by pressure, not by impact or blow. The boiler-pressure should 
be varied to suit the size of the rivets being driven, and main- 
tained at a uniform pressure during the entire work. A good 
steam-riveter should drive ordinary sizes of rivets ten times as 
rapidly as a single gang of riveters working by hand, notwith- 
standing the time and labor required in the handling and ad- 
justment of the boiler, the rivet, and the machine. The lighter 
machines are compelled to strike a blow : this gives less satis- 
factory and far less reliable work than when the machine has 



CONS TR UC Tl ON OF S TEA M-B OILER S. 



407 



sufficient power to head up the rivet by steady pressure. In 
working this machine the rivets are inserted from the outside 
of th^ boiler, instead of, as in hand-riveting, from the inside. 
The boiler, suspended in slings attached to a crane, is drawn 
up to the riveting-hammer, and the pressure heads up the rivet 
in a moment, and the steam-pressure is retained until the rivet 
is cool. The charge of steam used in riveting is sometimes 
utilized in its expansion to draw back the ram. 





Fig. 100, 

To drive rivets by hand, two strikers and one helper are 
needed in the gang, besides the boy who heats and passes the 
rivets; to drive each f-inch rivet an average of 250 blows of the 
hammer is needed, and the work is but imperfectly done. 
With a steam riveting-machine, two men handle the boiler and 
one man works the machine. 





Fig. ioi. 

Where the plates of which portions of a boiler are com- 
posed meet at right angles, the connection may be made by 
either of the methods exhibited in the illustrations above : as 
by angle-iron (Fig. 99) ; by a T-iron, when stiffness is desirable 
in the transverse plane (Fig. 100) ; or by flanging (Fig. loi). 

In order to exhibit the relative advantages of machine and 
hand riveting, we have in Fig. 102 an illustration of two plates 



THE STEAM-BOILER. 



riveted together, the holes of which were purposely made so as 
not to match perfectly. Rivet a was put in by the steam-riveter, 
and b by hand. The machine-rivet fills the hole completely, 
while the hand-rivet is very imperfect. 

The hand-rivets fill up the holes immediately under the 
head formed by the hammer; but sufficient pressure could not 
be given to the metal by hand to insure equally good work. 

The hydraulic riveting-machine compresses without a blow, 
and with a uniform pressure, variable at will ; each rivet is 





Fig. I02. — Hand and Machine Riveting. 



Fig. 103.— Accumulator and Pump. 



driven with a single movement, under complete control. The 
pressure upon the rivet after it is driven is maintained, or the 
die is retracted, as may be desired. This machine consists of 
a riveting-die attached to a piston in the compressing cylinder; 
this cylinder communicates with an accumulator through a 
valve moved by the operator. The work is performed without 
a blow ; the pressure is always uniform, and can be adjusted by 
the weights applied to the accumulator; it may be maintained 
as long as desired, or the riveting-die can be retracted as soon 
as the rivet is finished. The succeeding diagrams illustrate this 
system.* 

* Supplied through the courtesy of Messrs. Sellers & Co. 



I 



CONSTRUCriON OF STEAM-BOILERS. 



409 



Cold-riveting can be successfully adopted on light work when 
the best material can be obtained in the rivets, and is preferred 
where choice is allowed on account of the greater certainty in 
regard to quality of rivet and the freedom from risk of injury 
by heat. 

Steel rivets must be worked more rapidly than iron. 

The accumulator is an essential part of the system: in it 
water is kept under pressure by means of a pump, or otherwise. 
The chamber of the accumulator is closed at one end, and to 
the other end is fitted a stuffing-box through which a weighted 




Fig. 104. — Heavy Lap. 

plunger rises or falls as the quantity of water in the chamber 
increases or diminishes. By varying the load upon the plunger, 
the pressure upon the water in the accumulator-cylinder is ad 
justed. The water under pressure in the accumulator is there 
stored ready for use, and is conveyed through suitable pipes to 
the compressing cylinder of the riveting-machine, so that when 
the valve is opened the water flows into the cylinder, forcing 
the riveting-dies upon the rivet, and finishing the work with 
such force as the accumulator has been gauged to produce. 
The very high pressure at which hydraulic machines are 
operated, as compared with steam-riveters, makes the cylinder 
smaller and the machines less cumbersome. The hydraulic 
riveting-machine can be used wherever power by belt is obtain- 
able, and the pumps and accumulator may be placed at any 
point most convenient for the application of the power. In 
bridge- and ship-building the portable hydraulic riveter is com- 
monly employed. 



4IO 



THE STEAM-BOILER. 



The adjustment of laps and of courses, where the metal is 
thick and construction intricate, often demands much ingenuity 
on the part of either the designer or the builder of the boiler. 
Fig. 104 illustrates the usual arrangement in the shell of marine 
boilers of the Scotch type, where, as is customary, butt joints 
are employed with double riveting. 

The following sketches illustrate some of the best forms of 
joint in standard construction, beginning with the single-riveted 
joint of everyday use, and followed by various forms of double 
and triple riveting. 




CONSTRUCTION OF STEAM-BOILERS. 



41 r 



These joints are all proportioned as for steel, and a strength 
is assumed of 5000 pounds per running inch, the factor of safety 
being taken as 8, or for 8000 pounds if the factor be dropped 
to 5: 

The second of the group shows the junction of four over- 
lapping plates; and the third the method of arranging the 
covering-strips or "cover-plates." 




Where, as should always be the case, steel plates are drilled, 
or are punched and the holes sufificiently enlarged by counter- 
boring or reaming and the plates finally well annealed, no al- 



412 



THE STEAM-BOILER. 



lowance need be made for loss of strength in the metal be- 
tween the plates. 

The best makers of boilers endeavor to reduce the number 
of seams to a minimum, as well as to make those retained of 
uniform and ample strength. Double-riveted longitudinal 
seams are becoming constantly more common, and in some 
cases welding is resorted to with great success. The latter 
plan permits the securing of perfectly cylindrical courses or 
rings of plates. It seems not improbable that welding may 
ultimately become the usual method of making all joints. The 



2% , J/ : 1% 



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TRIPLE RIVETED. 






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lap-joints are disappearing in good designs, and the butt-joints, 
single and double riveted or other, are taking their place. 
In these cases the cover-plates, or covering strips, or straps, as 
they are variously called, should be cut from plate, and in such 
manner that the grain shall run parallel with the direction of 
stress. 

Welding, if it can be safely relied upon, offers so many ad- 
vantages over riveting, that there can be no question that it will 
in time supplant entirely the older method of uniting the parts 
of boilers. It has been the practice of a few makers to employ 
this system for many years, and the use of welded seams is slowly 
but steadily increasing. A good weld gives more nearly the full 



CONSTRUCTION OF STEAM-BOILERS. 413 

strength of the iron than can any arrangement of rivets, and en- 
ables all risks arising from defects in workmanship peculiar to 
riveting, such as drifting or careless chipping and calking, and 
such* as cold-hammering, to be avoided. It permits dispens- 
ing with calking entirely, and consequently the avoidance of the 
grooving or furrowing which so often proves dangerous. It is 
also possible to reroll the course or ring of welded plates, and 
thus to secure greater accuracy of dimension and perfection of 
form than could be obtained with riveted work. 

Welding is less likely to prove unreliable in flues than in 
shells of boilers ; as the steam-pressure there tends to force the 
parts together, rather than to separate them, as in the latter 
case. Great experience is in any case demanded, as well as 
great care and skill, in making long lines of weld, such as are 
required in this work. It is stated by Mr. Adamson, who has 
been one of the most successful makers using the process, that 
the metal must be of the best possible quality, and that steel 
containing enough carbon and other elements to perceptibly 
harden it cannot be safely employed. 

192. Flues and Tubes are set after the parts of the boiler 
are assembled, or in the construction of the tube-boxes and 
" connections." The flue is commonly riveted into the flanged 
opening cut into the two flue-sheets to receive it ; the tube is 
"expanded" into the tube-sheet by means of a "tube- 
expander," of which there are many kinds ; which tool forces 
out the tube into metallic and firm contact with the hole bored 
to receive it, and at the same time expands it a trifle on each 
side the sheet, and thus tightens its hold and gives it the 
effect of a stay, while still further insuring against leakage. 
Care must be taken to avoid too great expansion, as the tube- 
sheet is sometimes strained and weakened by excessive stretch- 
ing, and the tube itself is sometimes split. Properly set and 
expanded, a tube makes an exceedingly effective stay. A 
locomotive tube should safely carry 3000 pounds (1360 kgs.) 
and a marine boiler tube, of double the diameter, 5000 pounds, 
(2268 kgs.), or the full boiler-pressure ordinarily carried. For 
very high pressures, as now often attained with three and four 
cylinder " compound " engines, stay-tubes are introduced at in- 



414 



THE STEAM-BOILER. 




Okd 



Fig. io6.— Staying Flat Surfaces. 



tervals which are made of heavier iron, and have nuts screwed 
on the outside to sustain the excessive pressure. Many build- 



CONSTRUCTION OF STEAM-BOILERS. 415 

ers prefer not to bead over the ends of the tubes, fearing that 
the operation may loosen them and cause leakage. The ends 
of the tubes are annealed before expanding them. 

In laying out the flue or tube sheets, the centres are located 
by reference to the drawings, and the outline of the hole is laid 
out by the dividers. For flue-sheets, a row of small holes is 
drilled around the circle, marking the opening to be made ; the 
centre part is cut out, the opening trimmed and flanged, and 
the sheet is then ready to receive the flue. Tube-sheets are 
similarly laid off, a small hole drilled at each centre, and the 
hole then " counterbored " to the required size and the edges 
of the enlarged holes smoothly rounded to prevent cutting the 
tubes when expanded in place. 

Ferrules are often driven into the tube-ends, partly to give 
greater tightness, partly often to reduce the draught-area when, 
as sometimes occurs, it is too great. 

Staying is variously practised, and marine-boilers especially 
exhibit a great variety of methods. Fig. 106 illustrates a 
somewhat peculiar method of staying adopted in the boilers of 
the U. S. S. Nipsic. A set of gusset-plates is riveted to the 
shell, and the connection is stayed to them by means of lugs 
riveted to both. The long stay-rods running lengthwise of the 
boiler are connected to these gusset-plates. Other gusset-plates 
stiffen the junction of the adjacent parts of the shell above 
the connection. The water-spaces are stayed by riveted stay- 
bolts in the usual manner. 

Fig. 107 illustrates the staying of the heads of the boilers 
of the U. S. S. Monadnock. 

Fig. 108 exhibits the method of staying adopted in the 
boilers of the U. S. S. Miantonomoh, which differs from the 
more common practice in the manner of fastening the heads of 
the stay-rods. The eyes to which the rods are attached at 
the end are made fast to the shell by means of bolts passing 
through the plates and held by nuts on the outside. 

The usual method of securing the stay-rods and '' crow- 
feet " in marine-boiler construction is seen in Fig. 109, as prac- 
tised in the boilers of the U. S. S. Terror."^ A set of i-irons is 

* Shock on Boilers, 



4i6 



THE STEAM-BOILER. 




Fig. 107.— Staying Flat Surfaces. 




Fig. io8. — Staying Flat Surfaces, 



CONSTRUCTION OF STEAM-BOILERS. 



417 



riveted on the inside of the shell which gives an anchorage for 
the crow-feet to which the stay-rods lead, the connections being 
made by bolts in shear. 

Fig. no represents the method of staying adopted in the 
boilers of the S.S. Lord of the Isles to secure the heads. 

193. Chipping and Calking seams after they are riveted 
up is a process which is relied upon to insure against leak- 
age. The workman, with hammer and chisel chips the edge 
of the lap smoothly from end to end — sometimes only on the 
outside, but often, if accessible, on the inside, and thus ob- 
taining a smooth edge; then drives a blunt " calking-tool " 
against it, and thus expands the metal against the opposite 
plate, and securing metallic contact closes every leak. 




Fig. 109.— Staying Flat Surfaces. 

The process of chipping is a dangerous one, and the score 
produced by the chisel as its corner marks the under sheet has 
been often known to lead to the formation of a groove or a 
crack, and later to explosion. Planing the edge before final 
assembling and riveting up is much to be preferred. The use 
of the calking-tool has sometimes resulted in similar injury; 
and split-calking, which consists in driving the edge of a chisel 
into the edge of the sheet and thus splitting it slightly and ex- 
panding the lower part against the adjacent sheet, is advised as 
a safer plan. The Connery system, regarded by many as very 
much better than either of the preceding, is similar to the last ; 
27 



1 



4i8 



THE STEAM-BOILER. 



but a round-nosed tool is employed which makes a smooth, 
semi-cylindrical groove instead of a sharp crack. The expand- 
ing effect is also felt further back under the lap, the seam is 
thus tighter and more permanently so, and the use of the tool 
is not liable to injure the lower sheet. 




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-Staying Flat Surfaces. 



In European practice, even where the builders have not 
gone so far as to adopt the system of calking with a round- 
nosed tool, they have very generally substituted for the old 
and dangerous form of calking-tool a wider-edged tool called 
the fullering-tool, and the specifications usually prescribe ful- 
lered seams as well as planed edges. No calking-tool should 
ever be permitted to be used which has a sharp edge or corner 
that may by careless handling be made to cut, or even mark, 



the sheet at the edge of the lap. 



CONSTRUCTION OF STEAM-BOILERS. 419 

* Butts are calked with a tool which makes a depression on 
each side the line of junction, expanding the two sides into 
contact and making that line tight. It is customary with some 
makers to calk around* the heads of rivets, and when found 
leaking this process is resorted to as a remedy. Calking should 
not be done while the boiler is under pressure, and should be 
very carefully done at all times. 

The '' concave" calking, so-called, is exhibited in the ac- 
companying figure, which shows the difference in the effect 
of the new and old methods upon the sheet. The plate is 
shown, as bent after the operation, to determine the extent to 
which injury of the plate may have been incurred. On the left 
is seen the action of the concave system, the effect of the tool 
being somewhat more marked than is customary, but perfectly 
representing samples in possession of the Author. On bending 




Fig. III. — Concave and Common Calking. 

down the sheet, as shown, it is seen to be quite sound, and en- 
tirely unaffected by the action of the tool. On the other hand, 
the ordinary tool, as commonly used and as illustrated on the 
right in the same engraving, is almost invariably found to pro- 
duce a slight indentation of the sheet along the edge of the lap, 
and then to cause a tendency to crack when the sheet is flexed 
by the changing temperatures of the boiler and accompanying 
strains. By this method either the edge of the tool or the 
edge of the lap is liable to produce a dangerous groove, at 
once or after corrosion has progressed somewhat. The more 
rational system gives a broad band of metallic contact between 
the two sheets, and makes the joint tight without injury to 
the structure." 

In using the " round-nosed " calking tool, the followii]g 
directions should be observed : 

* Journal Franklin Institute, 1S74. 



420 



THE STEAM-BOILER. 



Chip or plane the plates to an angle of about iio°, seeing 
that the seams are perfectly close inside and outside. Apply 
the tool in the usual manner, forming a channel, and always 
keeping the burr between the tool and plate, and calk until 
found solid, smooth, and brought to a feathered edge, free from 
pin-holes. Do not cut off the burr, as it may injure the under 
plate. Upon testing, if pin-holes are found, apply the same 
tool as before, until made perfectly tight. The convex tool 
should taper about two inches from the point, which is about 
half an inch wide, otherwise perfectly straight, save when un- 
avoidable, and ground to a radius that will finish the concave 
channel to about one half the bevelled edge ; if too wide it will 
thicken the edge ; if too small it will wedge it off. 

194. Assembling is the process of fitting, and finally rivet- 
ing permanently together, all the details and members, which, 
separately constructed, are finally brought together to make the 
complete structure. The shell, the tubes and their tube-sheets, 
with the front and back connections and the steam-drum, are 
the several principal parts thus dealt with. The shell is first 
set in position and riveted up ; the flues or tubes and connec- 
tions are next finished, placed in their proper position within 
the shell, and riveted into place ; the drum or dome is attached ; 
and, finally, all minor details are added, and the boiler is ready 
for examination, test, and finally for calking and '' finishing." 

195. Inspection of the work should take place, not only 
when the boiler is reported completed, but should be kept up 
constantly throughout the whole period of construction. 
Where extensive contracts are filled, it is usual for the pur- 
chaser to have a skilled inspector constantly employed to see 
that the material introduced is in accordance w^ith the contract ; 
that the construction is precisely what is called for by the 
drawings and specification, the work well done, and the whole 
properly put together. 

A special inspection is usually provided for, to take place at 
completion and before acceptance. At this time the inspector 
very carefully and minutely examines the boiler inside and out, 
overhauling the braces and stays, their connections with the 
shell and other parts, and their welds and fitted parts ; he 
observes the character of the riveting, the method of attach- 



CONSTRUCTION OF STEAM-BOILERS. 



421 



ment of the various accessory members ; the valves, cocks, and 
gauges, if attached ; and every detail, great or small, comparing 
all with the specifications and drawings, and noting any defect, 
either in general construction or in workmanship. Any defec- 
tive material or bad work is condemned, and must be replaced 




Fig. 112.— Defective Pinning. 



by good material and with better workmanship. The final in- 
spection proving satisfactory, the boiler is tested. 

The defects sometimes revealed by inspection are flaws in 
the iron in parts not readily seen ; inferior iron in concealed 
portions of the boiler ; cracked flanges or laps, either in lines 



422 



THE STEAM-BOILER. 



from rivet-hole to rivet-hole, or from the rivet to the edge of the 
plate; ''unfair" or "half-blind " rivet-holes; weak and narrow 




Fig. 113. — Correct Construction. 

laps ; injury by calking or by chipping ; laps not well closed ; 

narrow water-spaces; injured tube-^ends ; loose and badly set 

and fitted braces and 
pins ; omitted stays or 
braces ; and minor de- 
fects. 

To ascertain whether 
a sheet is of the right 
thickness, a small hole 
is sometimes drilled at 
the suspected point. 
The connecting of 
stays should be con- 
demned if not as in 
Fig. 113; they are 
sometimes found as 






0000 


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9 « 






Fig. 115. 



Fig, 116. 



dangerous as the case illustrated in Fig. 112. 

The junctions of plates meeting at the intersections of seams 
are given the shape seen in the accompanying figures, the first 
showing the junction of three sheets as where the longitudinal 



CONSTRUCTION OF STEAM-BOILERS. 423 

and transverse seams meet in overlapping courses, the middle 
plate being thinned to give proper bearing. 

196. Testing" Boilers, when under inspection, at the time 
of acceptance, usually consists simply in filling them with cold 
water, applying a pump, and subjecting them to a pressure ex- 
ceeding that at which they are to be used. It is better to warm 
the water to the boiling-point nearly, as the pressure then 
affects a boiler more nearly as under the conditions of actual 
use. The temperature should not exceed the boiling-point 
under atmospheric pressure, as an explosion or serious rupture 
might follow the revelation of a defect — a result which has 
actually occurred in more than one instance. 

The pressure should be applied very carefully and steadily, 
and the steam-gauge watched to detect any sudden drop of 
pressure which would indicate yielding. The breaking of a 
brace is usually revealed by a sharp report. Gradual yielding 
is shown by a cessation of rise of pressure, or by its falling off. 
Leaks show themselves whenever seams have not been made 
tight, and are traced out by trickling drops or running streams, 
and. are marked with chalk or a pencil for later calking. The 
connection of large steam-drums or domes with the shell are 
apt to show weakness, and should be carefully watched as pres- 
sure rises. 

The pressure is finally relieved, the boiler emptied, all leaks 
stopped, and the test repeated if the result is not satisfactory. 
In filling boilers, care should be taken to run them full of 
water to the very top of the safety-valve case ; as any con- 
fined air might make trouble. 

Testing a boiler by filling it to the safety-valve with cold 
water and then starting a fire is advised by some writers as a 
very safe method ; since the pressure can be run up, if the 
boiler is tight, to any desired point without exceeding the boil- 
ing-point under atmospheric pressure, and thus without danger 
in case of a weak spot revealing itself. The temperature should 
not be allowed to go higher than that limit, as a boiler filled 
with water at the temperature due a high steam-pressure is 
more dangerous than when under steam at the same pressure. 

197- Sectional Boilers are constructed, so far as .composed 



424 THE STEAM-BOILER. 

of riveted work, precisely as are other boilers ; but they are 
usually constructed mainly of nests of tubes, connected by cast 
or forged '' headers," which are fitted together with machined 
or '' faced " joints, and held by bolts. Each header has its 
tube-end either screwed or expanded into it, or in some cases 
simply slipped into place and made tight by packing. In these 
boilers the special precautions to be observed are to see that 
the joints are well made and permanently tight. The facing 
off should be so perfectly done that a thin coat of red-lead 
paint, at most, should be all that is necessary to make the 
joints tight against any steam-pressure. The best makers 
do not even use this precaution. 

198. Transportation and Delivery are effected usually by 
the maker. Small boilers are simply loaded on strong wagons 
and carted off to the place at which they are to be delivered. 
Heavier boilers often require specially constructed vehicles, 
and the very cumbersome structures often seen where marine 
flue-boilers are employed are sometimes transported on skids 
and rolls as houses are moved. 

In hoisting boilers to place them on the vehicles on which 
they are to be transported, or in setting them, great care is re- 
quired to see that they are so handled as to introduce no 
risk of straining them. The best method of slinging them 
should be carefully studied ; the tackles used should be of 
more than ample strength, and no risk of sudden fall or change 
of position should be taken. 



CHAPTER XL 

SPECIFICATIONS AND CONTRACTS. 

199. The Purpose of Specification and Contract is to 

present a perfectly definite and exact statement of the charac- 
ter and extent of the work to be done : the forms and propor- 
tions of details, the time to be allowed in construction, and the 
amount and method of payments to be made by the purchaser. 
These documents are always prepared when any work of im- 
portance is to be done, and are signed by the two contracting 
parties, or by authorized representatives or agents. They con- 
sist of a formal contract, or statement of obligation, with spe- 
cifications describing all work to be done, and, where the case 
permits, of a set of drawings of everything to be made, in full 
and in detail ; which drawings form a part of the contract as 
well as of the specification. 

200. The Contract is an agreement in writing by which 
the one party to the bargain agrees to do a certain exactly 
specified work, and the other to make compensation in a cer- 
tain stated manner, and often with provision of penalties for 
failure to fulfil the terms of the contract. This agreement rep- 
resents as exactly and clearly as possible the mutual under- 
standing between the contracting parties in regard to all busi- 
ness relations involved in the performance of the work to be 
done. Everything needed to make the understanding definite 
is embodied in the contract. Advertisements, proposals, and 
preliminary agreements are often taken as parts of the contract, 
as well as drawings and specifications. These papers are made 
out in duplicate, and are signed by both sides, each retaining a 
copy. Where many interests are involved, representatives of 
each should sign and each should retain a copy. 

The essential conditions of a legal contract are that it shall 
be definite as to the obligations of both sides ; that the com- 



426 THE STEAM-BOILER. 

pensation be stated and valid ; that mutual consent be secured 
by voluntary act ; and that the parties in interest shall all sign 
of their own free will, and with a full understanding of the ob- 
ligation assumed. The mentally or legally incompetent cannot 
take part in any contract while such disability exists. The 
agreement is interpreted by its own reading, and the private 
intentions of the makers have no weight, nor have their mental 
reservations. The document is its own commentary and proof. 
Interpretations of terms are settled by the customary and habit- 
ual use of the term, and if technical, the word or phrase must 
be taken as having the meaning usual in the business. Obscur- 
ity of wording may vitiate the agreement. 

The duty of each party to the contract is to be separately 
defined and described. The contractor is bound to perform a 
specified work in a satisfactory manner, to complete it in a speci- 
fied time, and to accept a stated compensation, made in a man- 
ner and as to time clearly prescribed. The other party to the 
bargain is bound to make full compensation to the extent and 
in a manner stated, to aid in all proper ways in the carrying of 
the agreement into effect, and to at all times meet the con- 
tractor in a fair and helpful spirit. The work is the contractor's 
until paid for as prescribed by contract ; when so paid for, it 
becomes the property of the employer, who only then carries 
any risks on it, unless otherwise provided in the agreement. 

Penalties incurred by non-fulfilment of the terms of the con- 
tract are of the nature of a standing debt, and may be similarly 
held and collected. Non-fulfilment of an agreement by the one 
side does not necessarily give freedom from obligation to the 
other, except where such failure on the one side may interfere 
positively with the operations of the other. In statements of 
time, a day ends at midnight. No time being stated, the work 
must be done within what may be decided to be a '' reasona- 
ble" period. 

Action at law must usually be entered against one guilty of 
breach of contract within six years ; but the Statute of Limita- 
tions varies in different states. A guaranty and bond is some- 
times exacted to insure the completion of the contract ; but 
this is usual only in public work. 



SPECIFICATIONS AND CONTRACTS. 42/ 

201. The Form of Specification is such that every descrip- 
tive portion of the contract may be embodied in it, in a sys- 
tematic manner, in proper relative order, and in thoroughly 
definite shape. The character of materials to be employed ; 
the method of working them ; their final form ; the quality of 
the workmanship ; all instructions that may be needed in regard 
to the performance of the work — are given in the specifications. 
Since this document is that on which the intending contractor 
makes his offer, it must be absolutely complete, and as 
concise as possible. No detail should be omitted, and nothing 
should be left to be assumed or disputed. 

202. Specifications for Steam-boilers should not only com- 
ply with all the legal conditions of a sound contract, but should 
represent the best known practice of the time. They should 
be prepared by the designing engineer, and, with all drawings, 
advertisements, blank proposals, agreements, and intended form 
of contract, laid before the employer for careful discussion and 
final approval before any step is taken in the receiving of bids 
or the acceptance of proposals. They should include a full de- 
scription of the boiler to be built, with complete drawings, gen- 
eral and in detail; statements of the kind, make, and quality of 
the iron or steel to be used, the character of the workmanship 
to be demanded, the kind of tests to be applied, and every con- 
dition having a bearing on the subject. 

203. Sample Specifications are as follows, illustrating stan- 
dard practice in common forms of boiler-work. The first"^ is 
that of the tubular boiler already illustrated in § 15. 

Specification for a Horizontal Tubular Steam-boiler. 

Type. — Boiler to be of the horizontal tubular type, with overhanging- 
front and doors complete. 

Dinieiisioiis. — Boiler to be 16 feet 3 inches long outside, and 60 inches 
in diameter. Tube-heads to be 15 feet apart outside. 

Steam-dome to be 33 inches in diameter and 33 inches high. 

Tubes — How Set and Fastejied. — Boiler to contain 66 best lap- 

welded tubes, 3 inches in diameter by 15 feet long, set in vertical and 

* See A7n. Engineer, Nov. 1883: Specifications by the Hartford Inspection 
and Insurance Co. 



428 THE STEAM-BOILER. 

horizontal rows, with a space between them, vertically and horizontally, 
of not less than one inch (i"), except the central vertical space, which is 
to be two inches (2"), as shown in drawing. Tubes to be set sufficiently 
high from bottom of boiler to give room for man-hole and access to 
boiler underneath tubes, as shown in drawing. No tube to be nearer 
than 3 inches to shell of boiler. Holes through heads to be neatly 
chamfered off. All tubes to be set by a Dudgeon expander, and slightly 
flared at the front end, but turned over or beaded down at back end. 



FOR IRON PLATES. 

Quality and Thickness of Iron Plates. — Shell plates to be of an 

inch thick, of the best C. H. No. i iron, with brand, tensile strength, and 
name of maker plainly stamped on each plate. Tensile strength to be not 
less than 50,000 pounds per square inch of section, with a good per- 
centage of ductility. Heads to be of an inch thick, .of the best 
C. H. No. I flange-iron. 

FOR STEEL. 

Steel Plates. — Shell-plates to be of an inch thick, of homogene- 

ous steel of uniform quality, having a tensile strength of not less than 
6o,ooo pounds per square inch of section, nor more than 65,000 pounds 
with 45 per cent ductility, as indicated by the contraction of area at 
point of fracture under test. Name of maker, brand, and tensile strength 
to be plainly stamped on each plate. Heads to be of same quality as 
plates of shell in all particulars, of an inch thick. 

Flanges. — All flanges to be turned in a neat manner to an internal ra- 
dius of not less than two inches (2"), and to be clear of cracks, checks, or 
flaws. 

Riveting. — Boiler to be riveted with f-inch rivets throughout. All 
girth seams to be single-riveted. All horizontal seams and flange of 
dome at junction of shell of boiler to be double staggered riveted. Rivet- 
holes to be punched or drilled so as to come fair in construction. No 
drift-pin to be used in construction of boiler. A reamer to be used in all 
cases to bring the holes " fair." 

Braces.-r-'Y\\^x^ are to be twenty-two (22) braces in boiler — seven 

(7) on each head above the tubes, and six (6) on rear head and two (2) 
on front head below the tubes, as shown in drawing, none of which are 
to be less than three (3) feet long. Braces to be made of best round 
iron, of one (i) inch in diameter, and of single lengths. 

How Set and Fastened. — There are to be five (5) lengths of T-iron, 
four (4) inches broad and one half (i) inch thick. Three (3) being eight 

(8) inches long, Two (2) being fourteen (14) inches long, placed radially, 
and riveted with f-inch rivets to each head above the tubes, as shown 



SPECIFICATIONS AND CONTRACTS, 429. 

in drawing. There are to be four (4) lengths of T-iron, four (4) 
inches broad and one half (-|) inch thick, two (2) being six (6) inches 
long and two (2) being twelve (12) inches long, placed radially, and riv- 
eted on rear head below the tubes, also two (2) lengths, six (6) inches 
long, riveted on front head below the tubes, each side of man-hole, as 
shown in drawing. The holes for fastening the braces to these radial 
brace-bars are all to be drilled. The braces are to be fastened with suit- 
able jaws and turned pins or bolts, so as to realize strength equal to inch- 
round iron. Braces to be set as shown in drawing, and to bear uniform 
tension, and to be fastened on shell of boiler with two (2) f-inch rivets 
each. 

£)ome. — Dome to be constructed of same quality of iron or steel as 
heads of boiler, of an inch thick, and head to be of same quality of 

iron or steel as heads of boiler, of an inch thick. Dome-head to be 

braced with six (6) f-inch braces, reaching from head well down on 
shell, as shown in drawing, and fastened at each head with two (2) f- 
inch rivets. Opening from boiler into dome to be inches in diam- 

eter. There are to be two pieces of T-iron riveted on to outside of boiler 
shell, within the dome girthwise, one on each side of opening, as shown 
in drawing; also suitable drip holes to be cut at junction of shell and 
dome. 

Man-holes. — -Boiler to have two man-holes, each eleven (11) 

inches by fifteen (15) inches, with strong internal frames (as shown in 
drawing), and suitable plates, yokes, and bolts, the proportions of the 
whole such as will make them as strong as any other section of the shell 
of like area. One to be placed in front head underneath the tubes, and 
one to be placed on shell of boiler, as shown in drawing. 

Hand-holes. — Boiler to have one hand-hole, with suitable plate, 

yoke, and bolt, located in rear head below the tubes, as shown in the 
drawing. 

Nozzles. — Boiler to have two cast-iron nozzles, four (4) inches in- 

ternal diameter, one for steam and the other for safety-valve connections, 
securely riveted to head of dome, as shown in drawing. 

Wall-plates. — Boiler to have four cast lugs, two on each side, 

securely riveted in place, each twelve (12) inches long, with a projection 
of nine (9) inches from the boiler, the rear lugs each to rest on three 
transverse rollers, one inch in diameter, which are to rest on suitable 
cast-iron wall-plates, as shown in drawing, front lugs to rest on suitable 
wall-plates, without rollers. 

Blow-out. — For blow-out connection, one plate, one half inch thick, to 
be secured with rivets driven flush on inside of the shell, and tapped to 
receive a two (2) inch blow-pipe. 

Front. — Boiler to be provided with cast-iron front and all the 

requisite doors and fastenings for facility of access to tubes, furnace, and 



430 THE STEAM-BOILER. 

ash-pit. All to be of substantial construction, neat appearance, and 
close-fitting. 

Buckstaves — Grate-bars. — Boiler to be provided with 

buckstaves ; also all bolts, rods, nuts, and washers, anchor-bolts to ex- 
tend in setting beyond bridge-wall ; also bearer and grate bars (pattern 
to be selected); also cast-iron door, to be at least two (2) feet by three 
(3) feet and provided with liner plate, for back tube-door — and 
door fifteen inches by fifteen inches for flue for side or rear end. 

Fittings. — Boiler to be provided with one safety-valve, 

inches in diameter, one inch steam-gauge of standard make, three 

gauge-cocks properly located, also one glass water-gauge, a two-inch 
open-way blow-valve, and feed and check valves, each one and one 
quarter inch. Feed to be introduced into front bead of boiler, above 
tubes. Feed-pipe to extend well back towards rear of boiler, across 
tubes, and turn down between tubes and shell, as shown in drawing. 

Fusible Plug. — Boiler to be provided with a fusible plug so 

located that its centre shall be two inches above upper row of tubes at 
back end. 

Damper. — Boiler to be provided with a damper with suitable 

hand attachments, easily accessible at the front of the boiler, damper to 
be fitted to the throat of the smoke-arch, as near as practicable to the 
tube-openings, and of area equal to the cross-section of all the tubes. 

The size and description of parts to conform substantially to the de- 
tails of the accompanying plan. All the above to be delivered at 

and all the material and workmanship to be subjected to inspection and 
approval. 

The following are specifications for a marine flue-boiler for 



^SPECIFICATION FOR 1:- LUE-BOILER. 

There is to be one boiler of the flue and return-tube type, of the fol- 
lowing general dimensions : 

Extreme length. „ 13 feet. 

Diameter of shell 8 " 

Width of front 8 " 

Diameter of steam-chimney 5 " 

Diameter of steam-chimney lining 3 " 

Height of steam-chimney above shell 5 " 

* For very elaborate and complete naval specifications, see Shock's "Treat- 
ise on Steam Boilers." New York: D. Van Nostrand. 



PECIFICATIONS AND CONTRACTS. 431 

There are to be two furnaces, each forty two inches wide and six feet 
long. Bottom of furnace-legs to drop six inches below shell. Bridge-wall 
seven inches thick. Combustion-chamber of back furnaces in one twenty- 
four inches deep. Back connection twenty-eight inches deep. Front 
■connection twenty-eight inches deep. Furnace-crowns to be a semi- 
circle. To have two i6 inch, two 12-inch, two u-inch, and four 9-inch 
direct flues, all fifteen inches long, and ninety return tubes, seven feet 
ten inches long. 

All the horizontal shell-seams to be double riveted, also the bottom 
•course of steam-chimney where riveted to shell and vertical seams. 
Back part of furnace, where connected to shell, to be double-riveted one 
third distance around, the remainder of riveting about the boiler to be 
single. 

Thickness of Plates. — To be as follows : tube-sheets yV, shell of boiler 
(round part) f, bottom course of steam-chimney -^V' inside lining of steam- 
chimney f , the balance of the iron in the boiler to be -^-^, except bottoms 
of furnace legs, which are to be f. 

Material. — Furnaces to be of steel, and the balance of the iron in the 
boiler to be of the best C. H. No. i, and flange iron, and all stamped 
50,000 pounds T. S. All fiat surfaces to be braced 6|-inch centres, with 
hot sockets wherever practicable. 

Boiler to be fitted with man-hole in top of shell, also in front in the 
spandrels over furnace- crowns. Openings to be surrounded by a wrought- 
iron ring i\ inches wide by f inch thick, riveted to shell. Hand-holes to 
be cut in legs and every part where necessary to facilitate cleaning. Man 
and hand holes to be furnished with plates and bolts complete. 

Front connection to be fitted with wrought-iron doors, fitted with 
wrought-iron linings, and fitted with two registers. Furnace-doors to 
be of wrought-iron with cast-iron perforated linings, to be fitted with 
wrought-iron hinges, latches, etc., complete. A suitable opening with 
•door to be provided in back connection. 

Grates and Bearers. — Boiler to set on three cast-iron legs under fur- 
naces running the whole length, about 12 inches high, and fitted with 
supports for grate-bar bearers. Grates to be 6 feet long in two lengths. 
Ash-pans of cast-iron to be laid in brick and cement. Back ends of legs 
to be closed in with No. 10 sheet-iron. 

Shell of boiler to rest on a cast-iron saddle in two halves firmly 
bolted. 

Test. — The boiler before being hoisted into the vessel is to be sub- 
jected to a hydrostatic pressure of 100 pounds per square inch. 

Boiler Connections. — Smoke-pipe 36 inches diameter, and to extend 
16 feet above top of steam-chimney, to be made of No. 12 iron, to be 
finished with angle-iron top, bead-iron joints, six chain-stays and damper, 
iirranged to be operated from the fire-room. Lower part of smoke-pipe 



432 THE STEAM-BOILER. 

to be bolted to the steam-chimney, the inside lining being carried up for 
this purpose. Chain-stays to be provided with turn buckles to take up 
the slack. 

Steam-chimney to be encased with No. i6 sheet-iron and fitted with a 
stopping-cap in two halves. A chamber of cast-iron is to be bolted to 
the steam-chimney, containing the safety-valve and stop valve, each to 
be five inches in diameter, with top of trumpet shape. Surface and 
bottom blows to be provided witii screw stop-valve for the former and 
cock for the latter, secured on the boiler. Blows to be led out of the 
vessel below the water-line through a suitable valve. 

There is to be a feed-valve on each side of boiler in front, in con- 
nection with check-valve, one to be for the donkey and the other for the 
main feed-pumps, both to be of composition and 2 inches diameter. 
Gauge-cocks and glass water-gauge to be placed on a stand-pipe, con- 
nected to the boiler. Boiler to be covered witli i-^-inch felt, canvased 
and painted, felt to be secured with necessary bands around steam-chim- 
ney. 

Steam Pwnp. — To be an approved steam-pump with 2|-inch water- 
plunger, and fitted with hand-gear. To be connected with necessary 
receiving-pipes from bilge and sea cock, and delivery-pipes to boiler, over- 
board and for fire hose, each branch to be fitted with a proper screw- 
valve. Exhaust-pipe to lead overboard, awash with water-line ; all the 
donkey pump-pipes to be of wrought-iron, galvanized. 

The following is a general proposal-specification for " sec- 
tional boilers," purposely left somewhat elastic to admit all 
bidders : * 

Sectional Steam boilers. 

Boilers. — Proposals will be received for two (2) sectional or water- 
tube steam-boilers of nine hundred (900) superficial feet of heating-sur- 
face each, or eighteen hundred (1800) superficial feet of heating in the 
aggregate for both boilers. 

Details. — The proposals must be for the two (2) steam-boilers complete 
with cast-iron fronts, grate bars and bearers, ash-pit and side doors and 
frames, steam and water gauges, check and blow-oflf valves, safety-valves 
of the pop pattern, smoke connection for chimney, damper and rods^, and 
a steam main connected with the steam drums of the two boilers, together 
with all bolts, beam-columns and materials necessary for the proper 
erection of said boilers upon the grounds of the gas company in the city 
of Cincinnati. 

* Issued by the Cincinnati Gas Co., as prepared by Mr. J. W. Hill, 1883. 



SPECIFICATIONS AND CONTRACTS. 433 

Erection. — The proposals must embrace the construction, erection, and 
trimming of said boilers complete, excepting connection of steam-main 
with company's steam-pipe. The contractors to turn over the plants to 
the company ready for use. 

Tubes. — The tubes in the boilers shall be lap-welded, of three and 
one half (3.5) inches, or four (4) inches, external diameter (at the option 
of the contractor), of such length and arrangement in connection with 
steam and water drums as may seem proper to the contractor. 

Steam Drums. — The steam-drums shall be twenty-eight (28) inches 
diameter, of Otis or equivalent soft steel plates, of a tensile strength of 
seventy thousand (70,000) pounds per square inch of section, of three- 
eighths (.375) inch thickness, with double-riveted longitudinal seams, 
and furnished with heads corresponding in quality and strength with the 
steel shell. 

Steam Mains. — The steam-mains shall be eighteen (18) inches diam- 
eter, of Otis or equivalent steel plates, of a tensile strength of seventy 
thousand (70,000) pounds per square inch of section, of one quarter (.25) 
inch thickness, with double-riveted longitudinal seams, and with heads 
corresponding in quality and strength with the steel shell. 

Water Drums. — The water-drums may be of cast-iron or wrought- 
iron, at the option of the contractor, of sixteen (16) inches diameter, and 
shall be of same relative strength as the steam-drums. 

Sample Joint. — Each proposal shall be accompanied by a sample 
joint, such as will be used in connecting the tubes to the headers, or to 
the steam and water pumps ; and shall contain a detailed schedule (writ- 
ten or printed) of all the material dimensions of parts subject to strain, 
(pressure) and shall be accompanied by a scale-drawing [one and one 
half (1.5) inches to the foot] of front elevation, transverse and longi- 
tudinal sections, and plan of boilers set in brick-work ready for smoke 
connections with chimney. 

Chimney. — The company will furnish a brick chimney, properly 
located, octagonal in form, of an internal cross-section of twelve (12) 
superficial feet, increasing gradually in internal diameter from bottom to 
top, and ninety (90) feet six (6) inches high from level of boiler-house 
floor. 

Heating Surface. — The proposals must state exact heating-surface,, 
measured upon inner diameter of tubes, and outer diameter of steam- 
drums (or steam and water drums). 

Grate Surface. — Grate-surface and area of cross-section of smallest 
throat througii which the hot gases must pass to chimney, and area of 
cross-section of smoke connection with chimney to be stated. 

Smoke Holes. — (The openings one upon either side of stack to receive 
the smoke connections will have an area of six (6) superficial feet each, 
and will be two (2) feet wide horizontal diameter, and three and forty- 
28 



434 THE STEAM-BOILER. 

three hundredths (3.43) feet long vertictil diameter, with semicircular ends 
struck upon a radius of one (i) foot.) 

Fuel. — The fuel to be fired under the boilers will be " Breeze" or coke 
screenings, a smokeless fuel containing from twelve (12) to fifteen (15) 
per cent of non- combustible matter. 

Guarantees. — Each proposal must contain a guarantee of capacity of 
not less than four (4) pounds of steam per hour per superficial foot of 
heating-surface, with moderate firing; and shall contain a guarantee of 
economy of not less than eight (8) pounds of steam exclusive of water (if 
any) entrained from and at 212° Fahr. per pound of " Breeze." 

Test Trial. — Wlien the boilers are erected and completed, a test-trial 
for capacity and economy shall be made by the contractor, under direc- 
tion of the company. 

Failure to Comply. — Should the boilers fail to comply with the con- 
tractors' guarantees for economy or (and) capacity, or in any other respect, 
a reasonable time not in excess of sixty (60) days shall be given the con- 
tractor to remedy such defects; failing in which the boilers and all 
appurtenances belonging thereto and furnished by the contractor shall, 
at the option of the company, be removed within thirty (30) days from 
order of such removal. 

Ti7ne. — The proposal must name the time after acceptance required 
for completion of boilers as per invitation. 

Terms of Pay inent. — One half of the contract price for said boilers 
will be paid upon completion, and after the test-trial and acceptance as 
herein provided ; and the balance within thirty (30) days thereafter. 
The company reserves the right to reject any or all proposals submitted. 

The following are two dimension-specifications of boilers 
and locomotives as issued by the Pennsylvania Railway Motive 
Power Department : 



Standard P. R. R. Class " R" Freight Engine with Tender. 

Boiler material, . Steel. 

Thickness of boiler-sheets, dome, and extended smoke-box, . ^^^ in. 

Thickness of boiler-sheets, barrel, .... 

outside fire-box, 
" " " smoke-box, sheet under dome, 
and throat, 

Max. internal diameter of boiler. 



waist. 



Belpaire fire-box, 
Min. internal diameter of boiler, ) 

Height to centre of boiler, from top of rail. 

No. of tubes, ..... 



t m. 

6o| in. 

59 in. 

89 in. 

183. 



SPECIFICATIONS AND CONTRACTS. 



435 



nside diameter of tubes, 

Outside " " 

Tube material, 

Length of tubes between tube- sheets, 

External heating-surface of tubes, 

Fire-area through tubes, ..... 

Length of fire-box at bottom (inside), 

Width of '* " "... 

Height of crown-sheet, above top of grate (centre of fire-box). 

Inside fire-box material, 

Thickness of inside firebox sheets, sides, 

front, back, and crown. 

Thickness of tube sheets, 

Tube-sheet material, 

Heating-surface of fire-box, 

Total heating-surface, 

Fire-grate area, 

Max. diameter of smoke-stack, ) f^ .. 

\ Conical, 
Min. " " " S 



. 


2i 


in. 


. . 2i 


in. 


Wrought-iron. 


. I56i| 


in. 


1,564.24 sq. 


ft. 


5sq. 


ft. 


107 


m. 


42 


m. 


)ox), 51-I- 


in. 


. Steel. 




i 


in. 




tV 


in. 




i 


in. 


. 


Steel. 


166.8 sq. 


ft. 


1,731.04 sq. 


ft. 


31. 1 sq. 


ft. 


j26t 


in. 




18 


in. 



Standard P. R. R. Class " P" Passenger Engine with Tender. 



Boiler material, 

Thickness of boiler-sheets, dome, 

" barrel, and outside fire-box, . 
Thickness of boiler-sheets, slope, roof, waist, and smoke-box. 
Max, internal diameter of boiler, ) -ttt 
Min. ^Wagon-top, . . 

Height to centre of boiler from top of rail 
No. of tubes, . ... 

Inside diameter of tubes, .• 
Outside " " ... 

Tube material, .... 

Length of tubes between tube-sheets, 

External heating surface of tubes, 

Fire-area through tubes. 

Length of fire-box at bottom (inside), 

Width " .. « „ 

Height of crown-sheet above top of grate, centre of fire-box 

Inside fire-box material, ....... 

Thickness of inside tire-box sheets, sides, ' . • . 

front, back, and crown,' 

Thickness of tube-sheets, 

Tube-sheet material, 



Steel. 

tV in- 

f in. 

T6 in. 

56f in. 

53i in. 

861 in. 

240. 

If in. 

2 in. 

Wrought-iron. 

130J-V in. 

1,365.81 sq. ft, 

4 sq. ft. 

9 ft. ii| in. 

3 ft. 5f in. 

3 ft. 10 in. 

Steel. 

\ in. 

, A in. 

i in. 

Steel. 



43^ THE STEAM-BOILER. 

Heating-surface of fire-box, 164.39 sq. ft. 

Total heating- surface, 1,530.2 sq. ft. 

Fire-grate area, ....,.,. 34.8 sq. ft. 

Diameter of smoke-stack (straight), . . . . . . 18 in. 

Height of stack above top of rail, 15 ft. o in. 

204. Quality of Material and methods of test are often 
specified very minutely, and are sometimes settled by legal 
provisions. Thus the British "Admiralty" issue the following 
requirements, other than the ordinary tensile tests, for test of 
irons : 

Samples of B. B. iron i inch (2.54 centimetres) thick are to 
bend cold, without fracture, to an angle of 15° with the grain 
and 5° across the grain; -J- inch (1.27 centimetres) plates, 35° 
and 15° respectively; -f^ inch (0.48 centimetre) and under must 
bend 90° and 40°. When hot, plates i inch (2.54 centimetres) 
and under must bend 125° with and 90° across the grain. 

For B. iron, the requirements are : 



THICKNESS. 


ANGLE. 


ANGLE. 


Inches. 


Centimetres. 


With the grain. 


Across the grain 


I 


2.54 


10° 


5° 


i 


1.27 


30° 


10° 


-h 


0.48 and under 


75° 


30" 



Test-pieces to be 4 feet (1.22 metres) long with the grain 
and full width of plate across the grain. 

The plate should be bent from 3 to 6 inches (7.62 to 15.24 
centimetres) from the edge. 

The Admiralty tests for steel, are the following when selecting 
mild-steel ship-plates : 

Tenacity from 26 to 30 tons per square inch (4100 to 4700 
kilogrammes per square centimetre). Extension at least 20 
per cent in a length of 8 inches (19.3 centimetres). 

Longitudinal strips planed down, \\ inches (3.8 centimetres) 
wide, heated to low cherry-red, cooled in water 82° Fahr. (28° 
Cent.), must bend, in the press, to a curve of radius equal to 
one and a half times the thickness. 

Plates must be free from lamination and injurious surface 
defects. 

One plate in every fifty in any invoice is to be tested. 



SPECIFICATIONS AND CONTRACTS. 4^7 

Test-pieces to be 8 inches (20.32 centimetres) long, or more, 
and parallel. 

Weight is estimated at forty pounds per square foot for one 
inch thick, with a variation allowable of 5 per cent (lighter 
weight only) on plates of half inch thick or thicker. 

The same specifications apply to bulb, bar, and angle steel. 

Lloyd's rules allow for one ton higher tenacity and one half 
the bend specified by the Admiralty. Masts and yards are to 
be made of iron having a tenacity of 20 tons per square inch 
{3150 kilogrammes per square centimetre). 

In working, all plates and bars are to be bent cold when 
possible, and heating only resorted to when unavoidable. All 
parts that have been heated must be annealed as a whole, if 
possible, and if not, a little at a time. When necessary, long 
pieces may be made up of shorter ones with butted joints 
shifted and strapped securely. No pieces failing in the working 
can be used, but samples must be cut from them and forwarded 
to the Admiralty for examination. Work must be finished 
above a black heat. Hammering is objected to, and the 
hydraulic press used for bending when practicable. 

An American railroad makes the following specifications for 
materials supplied to the repair-shops : 

Specifications for Common Bar Iron. — Grain. — To be uni- 
form and fibrous, rather than granular in texture. Workma?t- 
ship. — All bars to be smoothly rolled and to be accurately 
gauged to size ordered. Tensile Strength. — To average 55,000 
pounds per square inch (3,867 kilogrammes per square centi- 
metre), and no iron to be received less than 50,000 pounds to 
square inch (3,515 kilogrammes per square centimetre). Work- 
ing Test. — A three-quarter-inch bar bent double, cold, to show 
no fracture ; the same bar, heated, to be bent and also to be 
drawn to a point showing no tendency to " red-shortness." 

Specifications for Stay-bolt Iron. — Grain. — To be uniform 
and of a fibrous nature. Iron to be soft and easily worked. 
Tensile Strength. — To be 60,000 pounds to the square inch 
{4218 kilogrammes per square centimetre). Working Test. — 
A bar three-quarter inch diameter to be bent cold, showing no 
flaw ; a piece of same diameter, having thread cut on it, m.ay 



43 S THE STEAM-BOILER. 

show opening when bent double, cold, but such opening should 
not extend more than one eighth of an inch in depth. When 
put into the boiler the metal should not become brittle 
when hammered down to form a head. 

205. The Duties of the Inspector are such as demand the 
utmost care, considerable skill, and a large amount of experience, 
together with a good judgment and absolute conscientiousness. 
He must also be a man of sufficient strength of character to do 
his duty by his employers, whatever influences may be brought 
to bear upon him to induce him to pass work or material which 
does not fully comply with the specification. He is expected 
to examine all material with a view to the determination, both 
of its full compliance with the terms of the specification and 
contract, and of its general fitness for the work. 

The first step in inspection is a careful measurement of the 
piece offered for examination, and a comparison with the draw- 
ing, model, pattern, or template, to ascertain if it is made 
exactly to size. 

Exact workmanship is often secured by a system of standard 
gauges. This is especially the case where machines are mad.e 
in large numbers. The modern method of manufacturing 
machinery for the market compels the adaptation of special 
tools to the making of special parts of the machines, and the 
appropriation of a certain portion of the establishment to the 
production of each of these pieces, while the assembling of the 
parts to make the complete machine takes place in a room set 
apart for that purpose. But this plan makes it necessary that 
every individual piece of any one kind shall fit every individual 
piece of a certain other kind without expenditure of time and 
labor in adapting each to the other. 

This requirement, in turn, makes it necessary that every 
piece, and every face and angle, and every hole and every pin 
in every piece, shall be made precisely of this standard size, 
without comparison with the part with which it is to be paired ; 
and this last condition com.pels the construction of gauges 
giving the exact size to which the workman or the machine 
must bring each dimension. 

Sizes being found right, the quality of the material is 



SPECIFICATIONS AND CONTRACTS. 439 

determined by examination and test; defective welds, lamina- 
tion, and cracks are found and condemned. A blow with a 
hammer often reveals unsoundness, and a laminated plate may 
be detected by suspending it and tapping it all over. If the 
defect appears on the surface, the sheet may be supported by 
the corners in the horizontal position, and water poured on it 
at the line indicating lamination, and then tapping it with a 
hammer. The liquid w^ill work into the sheet, lifting the surface 
lamina and revealing the extent of the defect. 



CHAPTER XII. 

THE MANAGEMENT AND CARE OF BOILERS. 

206. The Management of Steam Boilers, it may be stated 
generally, demands in the highest degree care, conscientious- 
ness, and unintermitted vigilance. The value of the property 
entrusted to the attendants is so great and the consequences of 
ignorance or neglect in operation are so serious, and may be so 
disastrous, that no possible excuse can be given for negli- 
gence on the part of the proprietor or his responsible repre- 
sentative, in securing intelligent, experienced, and trustworthy 
attendants, or on the part of the attendants, whether engineer 
in charge, fireman {'^ stoker"), or water-tender, in the manage- 
ment of the boiler. _, 

The care demanded, in ordinary working, to keep a full sup- ^j 

ply t)f w^ater, to preserve the fires in their most effective condi-' 
tion, to keep an even steam-pressure, an ample and unintermit- 
tent supply of steam, is such as tries the best of men ; but, 
added to this, it is imperative that the responsible man in charge 
of boilers have that presence of mind and readiness in action and 
promptness in expedients, in time of accident or of emergency, 
which is hardly less necessary than on the battlefield. In still 
further addition to these requirements, any person taking charge 
of boilers must understand so much of the trades of the boiler- 
maker and the machinist that he can if necessary make minor 
repairs, reconstruct his feed-apparatus, and refit the valves. He 
must know something of the nature and of the peculiar methods 
of combustion of all ordinary fuels, and enough of the principles 
of combustion to be able to realize the waste that may follow the 
introduction of an excess of air on the one hand or the produc- 
tion of incomplete combustion on the other, and enough of the 
nature and dangers of sediment and incrustation to understand 
the necessity of adopting the usual expedients for prevention. 



THE MANAGEMENT AND CARE OF BOILERS. 44 1 

He should know how to adjust the safety-valve, and should un- 
derstand its office and the liability to accident coming of its 
maladjustment or neglect. 

'Intelligence, experience, and conscientiousness are the best 
and only real insurance against accident. 

207. Staring Fires is an art which is not always familiar to 
even experienced firemen. With the soft coals it is only neces- 
sary to have a supply of some kind of kindling material that 
can be lighted by a match or a lamp, and to begin by building 
with it a small fire and then adding a little coal, and thus grad- 
ually increasing the flame-bed until the grate is fully covered 
with the burning fuel. On a large grate the whole area is usually 
first covered with fuel, from end to end and side to side, so that 
no currents of air can enter the boiler through the ash-pit, and 
so as to insure that all air entering the furnace may pass over 
the wood used in kindling the fire. The wood is placed on the 
front of the bed of coals, with oily cotton-waste, shavings, small 
chips, or other easily ignited material under it. The ash-pit 
doors are kept closed until the fire is fairly burning, so that the 
draught maybe concentrated on the point at which the flame is 
started. After a few minutes, the fire being well started, the 
upper part of the mass burning in front is pushed back over the 
grate, and the flame is rapidly communicated to the whole bed 
of fuel. When this is effected the ash-pit doors are opened and 
the fire managed in the customary way. The precaution must 
be taken to see that the air has free access to the boiler-room 
and to the furnace. 

The process just described will work well with anthracite 
coal ; but the operation is a slower one, and more wood is usu- 
ally required. 

Building a fire of wood and then gradually adding coal is a 
more expeditious method than the above, but it is less econom- 
ical. 

When it is known that steam will be needed the boiler 
should be at once closed up and filled, in order that, should a 
leak be discovered or a misfit occur in setting a man-hole or 
a hand-hole plate, time may be allowed to get it right without 
causing delay in getting up steam. A leak discovered after 



442 THE STEAM-BOILER. 

steam has been raised may sometimes be checked by driving in 
pine wedges. The rubber " gaskets" used in making the joints 
under man-hole and hand-hole plates may be " blackleaded " on 
one side to prevent their adhering to the boiler. All valves 
should be carefully examined before starting fires, and especial 
care should be taken to see that the safety-valves and the feed- 
check valves are in good order. All flues should be clean, and 
every part of the boiler and all its accessories should be given a 
last and thorough inspection. 

Before starting the fires the precaution should be taken to 
see that the fuel is not allowed to be placed in the furnaces 
until the boilers have been filled with water ; even the kindling 
material should never be permitted in an empty boiler. The 
fires should not be forced at the first, as hot gases passing over 
heating-surfaces in contact with cold water, and the sudden ex- 
pansion due to too rapid increase of temperature, may cause 
strain and leakage. 

208. The Management of Fires is an important but 
often neglected branch of instruction in fitting firemen for their 
special duties. The economy of boiler management is very, 
largely dependent upon the skilful handling of the fuel and the 
furnace. In general, the fires should be kept of even thickness, 
clear of ash and clinkers, and as clean at the sides and in the 
corners as elsewhere. The depth of the fuel is determined by its 
nature and size and by the intensity of the draught. Hard coals 
can be used in greater depth than soft, and large coal in deeper 
fuel-beds than small. A strong draught demands a thick fire, a 
mild draught a thin one. With a low chimney and natural draught 
small anthracite or fine bituminous coal may be most successfully 
burned in a layer but a hand's breadth in thickness ; while with 
large *' steamboat" coal of the hardest varieties and with a heavy 
forced draught, fires have been actually worked successfully of 
five times that depth, or more. The secret of success in hand- 
ling fires is to find the best depth of fire for the conditions 
existing ; to keep that thickness at all times, allowing for the 
ash that may accumulate ; to throw the fuel on the grate at 
such frequent intervals as will prevent the fire burning into 
holes or in irregular thickness at different points ; to introduce 



THE MANAGEMENT AND CARE OF BOILERS 443 

the coal so quickly and with such exactness of direction that no 
serious loss may occur from the inrush of cold air, and so that 
every shovelful should go precisely where needed, the place 
for the next shovelful being at the same instant located. The 
removal of ash is best done by means of a rake or other tool 
used under the grate, rather than by stirring and breaking up 
the bed of fuel by working through the furnace-door. The 
various forms of shaking grate now in use are often very effi- 
cient. For best working, the fire should usually be kept bright 
beneath, and the ash-pit clear. With light draught, however, 
and thin fires, it is sometimes advisable, if sufficient steam can 
be so made, to allow the fire to be less frequently raked out, 
and some accumulation of ash may be thus produced when 
working with maximum economy. 

'' Firing," or " stoking," as the replenishing of the fuel is 
called, must be done very quickly and skilfully to avoid serious 
annoyance by variation of steam-pressure and supply. Where 
several furnaces are in use this difficulty is less likely to be met 
with, as the fires may be cooled and cleaned in rotation. A 
skilful man will find it possible to keep steam very steadily with 
but two furnaces, even. 

Ash-pits should not be allowed to become filled with ashes, 
as the result would be the checking of the draught, the reduc- 
tion of the steaming capacity of the boiler, and loss of efficiency, 
even if not the melting down of the grates. It is customary 
at sea to clean out the ash-pits and send up ashes, throwing 
them overboard once in every watch of four hours, when in full 
steaming. If much unburned fuel is found in the ashes, it 
should be, if possible, cleaned out and returned to the fire, or 
used elsewhere. 

Cleaning fires consists in thoroughly breaking up the mass 
of fuel on the grate, shaking out all the ashes, quickly raking 
out all " clinker," as the semi-fused masses of ash and fuel are 
called, and, after getting a level, clean bed of good fuel, as 
promptly as possible covering the whole with a layer of fresh 
coal. This is done, usually, once in four hours at sea and twice 
a day on land ; but different fuels require somewhat different 
treatment. The work should be performed with the greatest 



444 THE STEAM-BOILER. 

possible thoroughness and dispatch, to avoid serious loss of 
steam-pressure. 

Mr. C. W. Williams' instructions for handling the fires, 
where bituminous coal is used and an air-supply above the fuel 
is provided, are substantially as follows : 

Charge the furnace from the bridge-end, gradually adding 
fuel until the dead-plate is reached and the whole grate evenly 
covered. Never permit the fire to get lower than four or five 
inches in thickness, of clear and incandescent fuel, uniformly 
distributed, and laid with especial care along the sides and in 
the corners. Any tendency to burn into holes must be checked 
by filling the hollows and securing a level surface. All lumps 
should be broken until not larger than a man's fist. Clean out 
the ash-pit so often that there shall be no danger of overheating 
the grate-bars. 

An ash-pit, brightly and uniformly lighted by the fire above, 
indicates that it is in good order and working well. A dark or 
irregularly lighted ash-pit is indicative of an uncleaned and 
badly working fire. The cleaning of the fire is best done, in 
ordinary working, by a ''rake" or other tool working on the 
under side of the grates, and not by a ''slice-bar" driven into' 
the mass oi fuel and above the grate. 

209. Different Fuels require different treatment. The 
principles just stated apply generally, but more, perhaps, to an- 
thracite coals. The soft coals are commonly so disposed on the 
fire that a charge may have time to coke and its gases to burn 
before it is spread over the grate ; liquid fuels must be so sup- 
plied that they may burn completely, at a perfectly uniform 
rate, and especially in such manner as to be safe from explosive 
combustion ; the same precaution is demanded with the gaseous 
fuels. Special arrangements of grate and a special routine 
in working may be, and often are, demanded in such cases."^ 

210. The Liquid and Gaseous Fuels are often and suc- 
cessfully burned in conjunction with solid fuels. In such cases 
the same methods are to be adopted and precautions observed 
in handling the latter as when burned alone. 

* For the peculiarities of these fuels and their use, see Chap. III. 



THE MANAGEMENT AND CARE OF BOILERS. 445 

The liquid fuels are almost invariably the crude petroleums. 
They are sometimes burned in a furnace in which they are 
allowed to drip from shelf to shelf in a series arranged verti- 
cally at the front of the furnace, the flame passing to the rear, 
with the entering current of air supporting their combustion. 
In many cases they are sprayed into the furnace by a jet of 
steam which should be superheated and at high pressure. The 
use of the steam is considered to have a peculiar and beneficial 
effect, possibly through chemical reactions facilitating the for- 
mation of hydrocarbons. The petroleums are all liable to 
cause accident if carelessly handled, and special precaution 
must be observed in their application to the production of 
steam. 

The gaseous fuels are seldom used under steam-boilers, except 
where " natural " gas from gas-wells is obtainable, or where a 
very large demand or the use of metallurgical processes justi- 
fies the construction of gas-generators. Even greater precau- 
tions against accidents by explosion are needed than with the 
liquid fuels. In burning gas, maximum economy is secured by 
careful apportionment of the air-supply to the gas-consump- 
tion, and especially in avoiding excess. The regenerator sys- 
tem is not generally economically applicable to boilers. 

211. The Solid Fuels, coal and wood, are burned in fur- 
naces which are proportioned especially for the intended fuel. 
With soft coals, the grate-bars are set closer together than for 
hard coals ; the provision for the introduction of air above the 
grate is larger, and a '' dead-plate" is usually provided on which 
to coke the coal. In the use of this device, the fresh fuel is piled 
on the dead-plate at the furnace-mouth, and then left until the 
next charge is to be thrown in ; the first is then pushed in and 
spread over the fire, and the second charge is coked. In some 
cases the fuel is replenished on one side of the fire at a time ; 
but oftener it is spread over the whole surface of the grate. 

A furnace for burning wood is deeper than one intended for 
coal. Wood burns so freely that the ingoing charges must be 
continually replaced by fresh fuel. 

212. The Operation of the Boiler, aside from the man- 
agement of the fires, in such manner as to make steam regu- 



^! 



446 THE STEAM-BOILER. 

larly and in ample quantity, mainly consists in adjusting the 
draught so as to make the production of steam keep exact pace 
with the demand, and in keeping the supply of feed-water as 
precisely proportional to the amount demanded, and thus pre- 
serving the water constantly at a safe level, and reducing to a 
minimum the danger, on the one hand, of uncovering heating 
surfaces, and on the other of causing heavy " priming" or 
foaming, or the production of wet steam. As the working 
conditions of a steam-boiler are always those of steady motion, 
constant vigilance and an undisturbed and unconquerable equi- 
librium of mind on the part of the attendants are essential to 
perfect safety and thorough efficiency. 

So long as the water is kept at the proper height in the 
boiler, the boiler itself being in good repair, safety is assured ; 
and if the steam-pressure can be held at the proper point, effi- 
ciency is equally well insured ; but to maintain a state of abso- 
lute safety and efficiency, it is essential that something more 
than careful feeding and skilful firing be practised. Every 
apparatus upon which the working of the boiler is in any de- 
gree dependent must be known to be in good order and abso- 
lutely reliable. Feed-pumps must be kept in good repair, well 
packed, and ready for service on the instant ; the safety-valve 
must, by at least daily trial, be seen to be in good working 
order ; the pressure-gauges must be frequently compared with 
a standard test-gauge to make certain that its error — it will 
usually have some error — is known and unimportant ; and the 
gauge-cocks and water-gauge glass — the latter, especially, is lia- 
ble to deceive — must be tried often and their reliability made 
evident. 

Blow-off and feed valves often leak, must be often exam- 
ined, and should be repaired or reground whenever perceptibly 
affecting the water-supply. A grain of sand or a chip under 
a valve has sometimes given rise to unfortunate results. 

In salt water, when using sea-water in the boilers, frequently 
blowing off from the bottom or a continuous discharge from 
the " surface-blow" or " scum-pipes" is essential to keeping the 
water so fresh as not to produce deposits or incrustation. The 
higher the '' saturation" permitted, however, provided that 



THE MANAGEMENT AND CARE OF BOILERS. 44/ 

common salt is not actually deposited, the less the expense of 
operation and the less the amount of lime-scale formed. About 
twelve times the quantity of salt found in sea-water is thus 
the maximum ; and three or four is probably as high as is 
safe, two thirds the water entering the boiler being converted 
into steam, the remaining third blown out into the sea again. 
And generally, if n represent the ratio of saltness of boiler to 
that of the sea, and m the ratio of feed-water blown out to that 
made into steam, 

n— \' in ^ 

and if the ratio of total feed-water to total evaporation is/, 

m 4" I n 

J: T 1/1 T * 



If large boiler-power is demanded, and a battery consisting 
of a considerable number of boilers is in use, one man should 
be detailed especially to see that the water is properly sup- 
plied ; he is called the ''water-tender." On a large steamer 
several are often employed, each caring for a set of boilers and 
supervising the firemen or '' stokers" and coal-handlers employed 
at his section. All these workmen should be carefully chosen, 
and known to be skilful and trustworthy. A careless or unskil- 
ful man will waste vastly more in bad firing than can be saved 
in the difference of wages between a good and an inefficient 
man. One good man should handle a ton of coal an hour — sev- 
eral times the value of his own wages — the total charges for the 
boiler-room amounting usually to about one fourth or one fifth 
wages, three fourths or four fifths fuel, and wear and tear. The 
coal-handler should be able to supply two to four firemen, 
according to distance of coal-bunkers and convenience of trans- 
portation. 

Firing — stoking — should be done with promptness and pre- 
cision during a few seconds, while the nearest man holds the 
furnace-door open. Every moment of needless delay allows 
great volumes of cold air to rush into the furnace, reducing the 



448 



THE STEAM-BOILER. 



efficiency of the boiler and causing strain by cooling the sur- 
faces just before exposed to gases of high temperature. The 
damper should be partly closed while working the fire. With 
a number of furnaces the order of opening the furnace-doors, 
may be systematically arranged, and a very noticeable saving 
thus effected. 

213. A Forced Draught is produced by the use of a 
blower or fan, or by the steam-jet. The former is the best 
method where practicable. In using the forced draught, the 
fires should be managed precisely as with a natural draught ; 
but the rate of combustion is so greatly increased that they 
must be made heavier, and the process of replenishing the fuel 
even more carefully conducted. The draught should— indeed 
must — usually be checked while adding fuel ; but where the 
closed fire-room or stoke-hole is adopted, or with the steam-jet, 
this is not absolutely necessary, though best both on the ground 
of economy and of safety. When the blast is driven into the ash- 
pit, care should be taken to open the ash-pit doors the instant 
the fan is stopped, or danger is incurred of melting down the 
grate-bars by the intense heat concentrated beneath them, un- 
tempered by the entering current of cold air. 

214. Closed and Open Boiler-rooms, with forced draught, 
have each their advantages and their special methods of man- 
agement. With the closed, air-tight, fire-room all air supplied to 
the fire passes through the room, ventilating it thoroughly and 
cooling it, while at the s^me time enabling the fires to be 
worked precisely as where a natural draught is employed. No 
peculiarities of management are introduced other than come of 
the rapidity of combustion. In providing for the opening and 
closing of the fire-room doors for entrance and exit of the at- 
tendants, a double system must be so arranged that one will 
always act as a valve to close communication with adjacent 
apartments. In putting on and taking off the blast the fan 
should be first ^' slowed down," the doors then opened, and finally 
the blower stopped. In putting on the blast these steps should 
be precisely reversed. 

With the open boiler-room and closed conducting passages 
leading from fan to ash-pit, the special precautions to be taken 



THE MANAGEMENT AND CARE OF BOILERS. 449 

are simply to open the ash-pit the instant the blast is stopped, 
or to start the blower the instant the ash-pit doors are shut. 

215. The Regulation of the Steam-pressure should be 
effected by varying the intensity of the draught by means of 
the damper at the chimney, or, where a forced draught is em- 
ployed, by properly adjusting the speed of the blower; it should 
never be attempted, except in a serious emergency, to regulate 
it by opening furnace, ash-pit, or " connection" doors. The 
latter method is certain to accelerate corrosion, strain the 
seams, and produce leakage of tubes, as well as to waste fuel. 
The rushing of currents of air, alternately cold and hot, through 
the flues and over the heating-surfaces has been found in some 
cases to have probably been the cause of injury leading to ex- 
plosion ; and the introduction of cold air over the fire is invari- 
ably a cause of serious loss of economy of fuel. 

Automatic dampers, if well made and reliable, are very use- 
ful. 

216. The Control of Water-supply should always be en- 
trusted only to experienced and proven men ; this is the main 
precaution to be taken in every case. The more uniform the 
supply, and the more perfectly the proper water-level is main- 
tained, the safer and the more economical the operation of the 
boiler. It is better that the feed-water be supplied continu- 
ously than to feed intermittently. Steam is then made more 
regularly, and of better quality ; the heating of the feed is more 
steady and more thorough ; the boiler itself suffers less from 
varying temperatures, either local or general ; and every opera- 
tion goes on more easily and more satisfactorily. 

The feed-pump, if used, should be amply large for cases of 
emergency, but should be ordinarily worked continuously and 
slowly ; the injector, if employed, should be of such size that 
it may never cease working while the boiler is in normal opera- 
tion ; and a second instrument or, better, an independent feed- 
pump, should be always ready for use should occasion arise. 
The necessity for watchfulness is greater with boilers having 
small water-space for their power, as the modern tubular and 
sectional boilers, than in the older types, in which the regulating 
effect of a large body of water is felt. 
29 



450 THE STEAM-BOILER. 

The first duty of engineer or of fireman, on taking charge 
of a boiler, for the day or for a watch, is to see that the water 
is at the right height ; and his constant care throughout the 
whole period for which he is responsible is to keep it right, and 
to provide against any contingency that may introduce a liabil- 
ity of its rising or falling beyond the intended and safe range of 
fluctuation. 

217. Emergencies are liable to arise unexpectedly in the 
operation of the steam-boiler and demand the highest qualities 
of mind and character on the part of him who may be called 
upon to meet them. Self-possession and coolness, with full 
control of every faculty, will usually enable the attendant to 
successfully meet any form in which they may appear, with the 
single exception of an explosion of the boiler ; for that case 
prevention is the only cure. Minor emergencies occur so fre- 
quently that the experienced engineer or fireman will generally 
meet them promptly and eft^ectively, and greater events often 
find him equally ready and prompt of action. Every attend- 
ant, whether in engine or boiler-room, should have constantly 
in mind the best course to take in the event of any accident ; 
and every intelligent and conscientious man will have often 
gone over, in his own mind, the methods and means by which 
he should attempt to prevent every probable accident, or to 
render its consequences as unimportant as possible. There is 
often no time to think, and whatever is to be attempted can 
only be done intuitively, on the instant, on the impulse of the 
moment, guided by earlier thought or earlier experience. This 
quality of readiness in emergencies is perhaps the most valua- 
ble of all those especially required in the management of 
engines, boilers, and machinery generally. 

218. " Low-water" is the most serious and trying of the 
conditions liable to arise in steam-boiler management. Once 
the water-level has fallen below that of the crown-sheet or the 
upper row of tubes, but one thing can be done — reduce the 
temperature of the furnace and flues as rapidly as possible to a 
safe point. To introduce a larger quantity of feed might cause 
a sudden and dangerous increase of pressure by flooding the 
overheated metal ; to attempt to haul out the fires might pro- 



THE MANAGEMENT AND CARE OF BOILERS. 45 I 

duce a similar effect by the momentarily higher temperature 
often caused by breaking up the bed of fuel, and by the pro- 
longed exposure of the already endangered metal it might 
cause the hot sheets or flues to give way. The proper course to 
pursue is at once to dampen the fires, preferably by quickly 
covering them with wet ashes. Coolness, promptness, and 
rapidity of action are the only safeguards in this case. With 
high steam-pressure, the danger is that the overheated and 
softened and weakened sheets may be forced out ; the intro- 
duction of the feed-water is in itself a less serious source of 
danger. The Author has many times, in experimental work, 
pumped water into a red-hot boiler,* but has only once seen an 
explosion so produced. He has experimentally allowed the 
water to be completely evaporated from an outside-fired boiler, 
and has then succeeded in covering the fires with ashes and re- 
fiUing the boiler without injury.f When the boiler has cooled 
down and no steam is forming, it will be safe to blow off steam, 
then haul fires, blow out the water, and examine to see if 
any injury has occurred. 

Dangers of this kind rarely arise where the gauges are kept 
in orders but carelessness in regard to the water-gauges and. 
gauge-cocks is said to be a more frequent cause of accident than 
all other causes combined. Equal care should be taken to 
see that the fusible plugs, if used, are clean and in good condi- 
tion. 

219. Priming or Foaming takes places whenever the quan- 
tity of steam drawn from the boiler exceeds that which can be 
liberated, dry, from the mass of water which it at the time 
contains. This action may be due either to forcing the boiler 
beyond its real capacity, or to the presence of foreign matters 
in solution, which tend to cause the retention of the bubbles of 
steam in the mass, and, when leaving it, to carry spray into the 
steam-space. A boiler will foam badly if the design and con- 
struction are such that a rapid circulation is not insured, sufficient 
to carry all steam made below the upper level freely to the sur- 



* In the work of the U. S. Commission on Steam-boiler Explosions, 1S75. 
i* This might not be as safe an operation with an inside f.red boiler. 



452 THE STEAM-BOILER. 

face, where it may be naturally discharged ; or where currents 
conflict ; and where a mass of water, entangled among the tubes 
or flues, finds no natural way of egress, laden as it is with the 
steam bubbles which convert it into foam ; and priming may 
thus occur, even when the boiler is working well within its rated 
capacity. Any boiler will foam if overworked. 

Priming is also produced by the presence of mucilaginous, 
oily, or other foreign matter in the water ; or by changing from 
a salt-water feed to fresh-water, and sometimes by the reverse ; 
by sudden and heavy demand for steam at the engine, or by 
suddenly and widely opening the safety-valve ; and by other 
causes less well understood. When foaming takes place, it often 
throws water from the boiler so rapidly and in such quantities 
that the engine may be liable to have a cylinder-head knocked 
out, and the height of the water-level in the boiler may be 
dangerously lowered. The instant such dangers arise the throt- 
tle-valve should be partly closed, when the water will usually 
immediately settle down in the boiler, making it possible to 
ascertain its height in the gauges. If dangerously low, — a rare 
occurrence, however,^ — proceed as already indicated ; if other- 
wise, the draught should be promptly lessened, the fires checked, 
and, by thus reducing the quantity of steam made, the pro- 
duction of foaming and its attendant dangers may be quickly 
stopped. If the cause is suspected to be dirty water, contin- 
uous feeding and blowing, and thus changing the water, should 
be resorted to to remove that cause of danger. With boilers 
heavily driven, as is usual at sea, and too common elsewhere, 
priming is always one of those contingencies which those in 
charge of the boilers must be prepared to meet. Where sur- 
face-condensers are used and the boiler is fed with water of un- 
changing and pure quality, foaming rarely occurs. 

The method of circulation of water in a plain cylindrical or 
other " outside-fired " boiler, an4 the course of the steam pro- 
duced, is well illustrated in the accompanying figure, the fire 
being assumed to be located at the left. The greater part of 
the steam made in the boiler is produced immediately over the 
fire, here assumed to be at the left, and rises at once, as seen, 
into the steam-space above, thus determining the circulation 



THE MANAGEMENT AND CARE OF BOILERS. 



453 



in currents rising at that end and falling at the rear end of the 
boiler. In all cases the rising currents are at the hottest part, the 
descending currents at the cooler portions of the boiler. Were 
a boiler so constructed as to be uniformly heated, an efficient cir- 
culation would not be obtainable. 

" False water" is a term applied to the apparent increase of 
volume of the water in a boiler when priming takes place. It 
may be imperceptible ; but it often causes an apparent rising c f 
the water-level to the extent of several inches. It is considered 
that a well-proportioned boiler should be capable of evaporating 
five times the volume of its own steam-space each minute 



-^u 







fififeiiS^^^S^: 








Fig. 117.— Circulation of Water and Steam. 



without serious priming ; but it is not thought wise to attempt 
an evaporation exceeding one half this amount. 

220. Fractures, whether of seams, sheets, or tubes, are liable 
to occur in all boilers; but the danger is diminished as the care 
taken in selection of material is the greater, the construction 
better, and the management more intelligent. Such injuries 
rarely occur so suddenly or are so extensive as to be imme- 
diately dangerous, and ample time is commonly allowed for their 
detection and safe remedy. Cracks in sheets or seams are re- 
paired by patching and in tubes by plugging each end, or by the 
removal of the sheet or tube. The duty of the attendant, for 
the moment, is to reduce steam-pressure at once, and as soon 
as possible blow off steam, to empty the boiler and to see it 



454 THE STEAM-BOILER. 

properly repaired — temporarily if necessary, but preferably per- 
manently. A blistered sheet should be treated as if fractured. 

221. A Deranged Safety-valve may sometimes cause dan- 
ger by making it difficult to reduce the steam-pressure or to 
keep it below a dangerous point. This is sometimes a conse- 
quence of the rusting of the stem or of the valve and its sticking 
to its seat, or in such a manner that an insufficient area for exit 
is obtainable. In such a case the steps to be taken are to check 
the fires, to reduce the production of steam, and to find other di- 
rections of egress, as through gauge-cocks, all available valves, by 
the engines taking steam from the boiler, and by means, even,, 
of their cylinder, water, and drip cocks, until the safety-valve 
can be made to work or until the steam can be disposed of ia 
other ways. If the valve be daily or oftener raised to its full 
height, no such danger will be incurred. 

222. The General Care of a steam-boiler demands much 
experience, some knowledge of the causes and the methods of 
prevention and of remedy of injury, and thorough reliability on 
the part of those to whom it is entrusted. Aside from the in- 
juries and the deterioration which occur in its daily operation, 
there are others which are to be anticipated quite independently,, 
and which may become even more serious when the boiler is 
out of use : these are principally the various forms and conse- 
quences of corrosion. Such general care includes the preserva- 
tion of the boiler against decay or loss of efficiency, the reten- 
tion of its setting in good repair, and the keeping in order of 
all its accessories and connections. 

223. The Chemistry of Corrosion has been studied by 
many distinguished modern chemists, and is now well under- 
stood. Corrosion of iron and steel and the changes which 
characterize that method of deterioration cannot go on in the 
air except when both moisture and carbonic acid are present, 
or unless the temperature is considerably higher than that of 
the atmosphere. When exposed to the action of free oxygen, 
however, under either of these conditions, the metal is cor- 
roded — rusts — rapidly or slowly, according to its purity. 
Wrought-iron rusts quickly in damp situations, and especially 
when near decaying wood or other source of carbonic acid ; 



THE MANAGEMENT AND CARE OF BOILERS. 455 

while steels are corroded with less rapidity, and cast-iron is 
comparatively little acted upon. The presence of acids in the 
atmpsphere accelerates corrosion, and the smoke of sulphur- 
charged coal, or smoke charged with pyroligneous acid, fre- 
quently causes the oxidation of out-of-door iron structures. 

The composition of the rust forming upon surfaces of iron is 
determined by the method of oxidation, but is principally per- 
oxide of iron. Calvert gives the following : 

Rust from Coxiway Bridge. Llangollen. 

FcaOs 93-094 92.900 

FeO 5.810 6.177 

Carbonate of iron 0.900 0.617 

Silica 0.196 0.121 

Ammonia traces traces 

Carbonate of lime 0.295 

A series of experiments made to determine the effect of dif- 
ferent oxidizing media, after four months' exposure of clean 
iron and steel blades, gave results * indicating that oxidation is 
principally due to the presence of carbonic acid with oxygen. 

When distilled water was deprived of its gases by boiling, 
and a bright blade introduced, it became in the course of a few 
days here and there covered with rust. The spots where the 
oxidation had taken place were found to mark impurities in the 
iron, which had induced a galvanic action, precisely as a mere 
trace of zinc placed on one end of the blade would establish a 
voltaic current. 

224. The Methods of Corrosion vary with circumstances. 
Kent has shown f that the rusting of iron railroad bridges is 
sometimes greatly accelerated by the action of the sulphurous 
gases and the acids contained in the smoke issuing from the lo- 
comotive, and that sulphurous acid rapidly changes to sulphuric 
acid in the presence of iron and moisture, thus greatly acceler- 
ating corrosion. Iron and steel absorb acids, both gaseous and 
liquid, and are therefore probably permanently injured when- 
ever exposed to them. 

Calvert experimented upon iron immersed in water contain- 

* Chefuical Nezvs, 1870-71. \ Iron Age, 1S75. 



456 



THE STEAM-BOILER. 



ing carbonic acid, in sea-water, and in very dilute solutions of 
hydrochloric, sulphuric, and acetic acids. A piece of cast- 
iron placed in a dilute acetic-acid solution for two years was 
reduced in weight from 15.324 grammes to 3^ grammes, and in 
specific gravity from 7.858 to 2.631, while the bulk and outward 
shape remained the same. The iron had gradually been dis- 
solved or extracted from the mass, and in its place remained a 
carbon compound of less specific weight and small cohesive 
force. The original cast-iron contained 95 per cent of iron 
and 3 per cent of carbon, the new compound only 80 per cent 
of iron and 1 1 per cent of carbon. Iron immersed in water 
containing carbonic acid was also found to oxidize rapidly. 
Iron exposed to the wash of the warm aerated water of the jet- 
condensers of steam-engines is often very rapidly oxidized, and 
the mass remaining after a few years often has the appearance, 
texture, and softness of plumbago, so completely is the iron re- 
moved and the carbon isolated. 

Mallett, experimenting for the British Association,"^ found 
the rate of corrosion of cast-iron greatly accelerated by irregu- 
lar and rapid cooling, and retarded by a slow and uniform re- 
duction of temperature while in the mould. 

The rate of corrosion is usually nearly constant for long 
periods of time, but it is retarded by removal of the coating 
formed by the rust, as if left it creates a voltaic couple, which 
accelerates corrosion. 

Hard iron, free from graphite, but rich in combined carbon, 
rusts with least rapidity, and with about equal rapidity in the 
sea as in the air, in an insular climate. Two metals of differ- 
ent character as to composition or texture being in contact, the 
one is protected at the expense of the other. Foul sea-water, 
as '' bilge-water," corrodes iron very rapidly. 

The rate of corrosion of iron is too variable to permit any 
statement of general application. In several cases the plates 
of iron ships have been found to be reduced in thickness in 
the bilges and along the keel-strake, at the rate of 0.0025 inch 
(0.06 millimetres) per year, as ordinarily protected by paint ; 



*Proc. Inst. C. E. 1843. 



THE MANAGEMENT AND CAKE QF BOILERS. 



457 



while it is stated that iron roofs, exposed to the smoke of loco- 
motives, have sometimes lasted but four years. 

The iron hulls of heavy iron-clads have sometimes been 
locally corroded through in a single cruise, where peculiarities 
of composition or of structure, or the proximity of copper or 
of masses of iron of different grade or quality, had caused local 
action. 

225. Durability of Iron and Steel. — Twaite"^" gives the fol- 
lowing as the measure of the probable years' life of iron and 
steel undergoing corrosion, assuming the metal to be uniform' 
in thickness. Thin parts corrode most rapidly. 



T'- 



W 
CL 



in which W\^ the weight of the metal in pounds, of one foot 
in length of the surface exposed ; L is the length in feet, of its 
perimeter; and C a constant, of which the following are values : 



VALUES OF c. 



Material in 



Cast-iron 

Wrought-iron 

Steel 

Cast-iron, skin removed 

galvanized 

" in contact with brass, copper, or gun-bronze 

Wrought-iron in contact with brass, copper, or gun-bronze. 



Sea Water. 



Foul. 



0656 
1956 
1944 
2301 
0895 



Clear. 



0635 
1255 
0970 
0880 
0359 



River Water. 



Foul. 



0381 
1440 

1133 
0728 

0371 



Clear, or 
in air. 



.0113 
.0123 
.0125 
.0109 
.0048 



Impure 
Air. 



.0476 
.1254 
.1252 
.0854 
.0199 



Average 
Sea Water. 



0.19 to 0.35 
0.30 to 0.45 



When wear is added to the effect of oxidization, the '' life" 
of a piece of iron or steel may be greatly shortened. If kept 
well painted, multiply the result by two. 

The mean duration of rails of Bessemer steel is, accord- 
ing to experiments in Germany, about sixteen years. Ten 
years of trial at Oberhausen, on an experimental section of the 



Molesworth, p. 32, 21st ed. 



458 THE STEAM-BOILER. 

line between Cologne and Minden, has shown that the renewals 
during the period of trial were J^."] per cent of the rails of iron 
of fine grain, 63.3 of those of cementation steel, 33.3 per cent 
of those of puddled steel, and 3.4 per cent Bessemer steel. 

226. The Preservation of Iron and Steel is accomplished 
usually by painting, sometimes by plating it. 

As the more porous varieties will absorb gases freely and 
some liquids to a moderate extent, Sterling has proposed to sat- 
urate the metal with mineral oil ; heating the iron and forcing 
the liquid into the pores by external fluid pressure, after first 
freeing the pores from air by an air-pump, or other convenient 
means of securing a vacuum in the inclosing chamber. 

Temperatures of 300° to 350° Fahr. (150° to 177° Cent.) 
and pressures of 1 3 to 20 atmospheres are said to be sufficient 
for all purposes. 

Voltaic action may be relied upon to protect iron against 
corrosion in some situations. Zinc is introduced into steam- 
boilers for the double purpose of preventing corrosion and of 
checking the deposition of scale. It is sometimes useful in the 
open air, where rusting is so seriously objectionable as to justify, 
the use of so expensive a preventive. The zinc itself is often 
quickly destroyed. 

Zinc has been used as a plating, or sheathing, on iron ships,, 
as by the plan proposed by Daft,"^ and in some cases with good 
results. 

Mallett has proposed the use of lime-water to check the 
internal corrosion of the bottoms of iron ships where exposed 
to the action of bilge-water, and uses a solution of the oxy- 
chloride of copper, or other poisonous metallic salts, in the 
paint applied externally, to check fouling and consequent 
oxidation; the amalgam of zinc and mercury is also some- 
times used to protect iron plates. 

227. The Paints and Preservation Compositions in use 
are very numerous : Coal-tar, asphaltum, and the mineral oils 
are all used, the latter having the advantage, in the crude state, 
of being free from oxygen and having no tendency to absorb it. 

The animal and vegetable fats and oils are used temporarily 
in many cases, and if free from acid, are useful. 



THE MANAGEMENT AND CARE OF BOILERS. 459 

Surfaces of iron are painted with red-lead and oil, with oxide 
of iron mixed with oil, or with oxide of zinc similarly prepared. 

Sterling prepares a varnish by dissolving gum copal in 
paraffine oil, placing the iron in it, and heating it under in- 
creased pressure. Iron vessels, tinned inside, which can be her- 
metically sealed, are used, heated by superheated steam. Scott 
uses the following mixture : 

Coal tar. . . 6 gallons. 

Black varnish 3 " 

Wood-tar oil 2 " 

Japanese glue , o . . i * ' 

Red lead 28 lbs. 

Portland cement 14 " 

Arsenic » 14 " 

The Author has used fish-oil as a preservative of steam-boil- 
ers out of use for long periods of time, with success, and has 
found some vegetable paints of unknown composition far more 
durable, when exposed to the weather, than red-lead and oil. 

" Iron paints" bear heat well, and are often better than any 
other cheap paint. Iron to be painted should first be carefully 
cleaned by scraping and washing, and then coated once or twice 
with linseed-oil. One pound of good oxide of iron paint should 
cover 20 square yards (16.7 square metres) of iron. 

Where practicable the Barff method of protection may be 
adopted for small parts. It consists in heating the iron or steel 
to be treated to a temperature of 500° Fahr. (260° Cent.) in an 
atmosphere of steam, and thus securing an even and imperme- 
able coating of the black (ferric) oxide. 

Where more complete protection is demanded, the iron is 
heated to 1200° Fahr. (649° Cent.), and is said to be thus made 
impregnable against the attack of even the acrid vapors of the 
chemical laboratory. 

Steam-boilers are preserved, in mass, against corrosion by 
various special methods. They are sometimes dried thoroughly 
by means of stoves, if necessary, and then closed up with a 
quantity of caustic lime in their water-bottoms or lower water- 

* Fouling and Corrosion of Iron Ships. London, 1867. 



4^0 THE STEAM-BOILER. 

spaces. Occasional inspection prevents injury occurring unde- 
tected in any case. 

When new boilers are stored they are usually painted inside 
and out. Air should be excluded from them by closing all 
man-holes, etc. Working boilers are best preserved by a thin 
coating of scale on their heating-surfaces. Mineral oils being 
used for lubrication of their engines, decay is far less likely to 
take place rapidly. Steel corrodes more rapidly than iron, and 
the common brands of iron corrode less than the finer. Zinc 
placed within boilers, and in amount one thirty-fifth the area of 
the heating-surface, was found, by the British Admiralty, to pro- 
tect them perfectly. A pound (0.45 kilogrammes) of carbon- 
ate of soda to every ton (or tonne) of coal burned is ordered 
to be pumped into boilers at sea, to give the water an alka- 
line reaction. Boilers of sea-going vessels average a life of nine 
or ten years. 

Boiler Coverings having for their object the protection of 
the external surfaces against loss of heat and from any inju- 
rious action liable to occur in consequence of their exposure, 
are of very various kinds, and are always considered the 
better the more perfect they are as non-conductors. Care 
should be taken, however, that they do not themselves cause 
injury more serious than that which they are designed to pre- 
vent. Hair-felt has been known to cause — possibly by some 
peculiar galvanic or electric action — observable acceleration of 
corrosion on the inner sides of the sheets to the exterior of 
which it has been applied, as, for example, where used to cover 
the steam-drums of marine boilers; mineral-wool, when con- 
taining sulphur-compounds, has been known to absorb moist- 
ure, and to thus cause rapid corrosion of parts with which it 
was in contact. When free from sulphur no such danger is 
incurred. 

The experiments of Mr. C. E. Emery give the following as 
the relative values of available covering materials:* 

* Trans. Am. Society Mech. Engrs., vol. ii., 1881. 



THE MANAGEMENT AND CARE OF BOILERS. 



461 



Non-Conductor. 


Value. 


Non-Conductor. 


Value. 


Non-Conducior. 


Value. 


Wood-felt 


1. 000 
.832 
• 715 
.680 
.676 




.632 

•553 

■% 

.470 




^6:! 


Mineral-wool No. 2... 


Pine-wood across fibre. 
Loam, dry and open... 

Slacked lime 

Gas-house carbon .... 


Coal-ashes 


•345 
.277 
.136 




Coke in lumps 

.\ir-space, undivided 


Sawdust 

Mineral-wool No. i... 



Hair or wool felt is injured by high temperature ; woods are 
liable to char, and all organic matters, in presence of grease and 
dampness, to take fire spontaneously. Asbestos is much used, 
as is also " rock-wool," which is less likely to absorb moisture 
than the " mineral-wool " from the blast-furnaces. Sand, ashes, 
and other earthy matters are often used to fill in over boilers. 
They are, however, liable to conceal and accelerate corrosion 
whenever leakage takes place beneath them. In all cases the 
values of successive layers of non-conductor decrease in a 
geometric ratio. Anything that will encage air in its pores is a 
good covering. Large boilers and their pipes, as designed by 
Mr. E. D. Leavitt, Jr., were covered with about two inches and 
a half of plaster and sawdust, and one inch of hair-felt outside 
that. The proportion of the mixture is about one part of 
plaster and two parts of sawdust. The plaster and the sawdust 
are mixed up like mortar. They are first put in together dry, 
and then wet and mixed up. For steam-pipes, the mixture is 
applied from one and a half to two and a half inches thick. 

For boilers, wooden battens f by 2\ inches wide are used. 
Between the edge of the batten and the boiler half an inch of 
the compound is put. These are fastened all around the boiler , 
then a band of hoop-iron is put around it, and filled between the 
battens with plaster. The practice of putting it on in little 
blocks about a foot square has been adopted. Outside of that, 
the specifications call for an inch of hair-felt and canvas.^ 

228. Leakage, and contact of damp portions of supports 
and setting, produce the most serious corrosion. A leak, once 
started, will keep everything near it damp, and thus cause 
acceleration of oxidation to a very marked degree. Where the 
leakage, or the dampness produced by it, finds its way between 
the iron of the boiler and the brickwork about it, there is no 



Trans. Am. Soc. Mech. Engrs., 1882. 



// 



4^2 rilE STEAM-BOILER. 

Opportunity of evaporation and drying the moistened surfaces, 
and the dampness thus held in contact with the metal promotes 
decay. When inspecting the boiler, care should be taken to 
detect every such cause of deterioration, and to immediately 
repair the injured part. It is well to so design and construct 
the boiler that there will be as little liability as possible to this 
kind of injury. 

229. Galvanic Action is liable to occur, and enormously 
to accelerate corrosion, either local or general, whenever a mass 
of brass, bronze, or copper, large or small, is in metallic contact 
with the boiler at any point, or with any of its connections. 
The brass tubes of a surface-condenser have been often knov/n 
to thus cause the ruin of a boiler in a few months, and very 
serious general corrosion in few weeks. Copper boiler-tubes, 
brass valve-seats, and any other minor part made of such 
electro-negative metals, may similarly cause local deterioration 
and leakage or weakness. The remedy is either to remove the 
cause of the trouble ; to protect the metal attacked, as by 
allowing it to become coated with a thin layer of incrustation ; 
or to counteract the effect of the electro-negative metal by in- 
troducing a mass of another element, as zinc, which is electro-' 
positive to both the iron of the boiler and the copper or other 
material producing the destructive action. In the latter case, 
the zinc will be corroded instead of the iron of the boiler, and 
must be occasionally renewed. 

230. Incrustation and Sediment are deposited in boilers, 
the one by the precipitation of mineral or other salts previously 
held in solution in the feed-water, the other by the deposition 
of mineral insoluble matters, usually earths, carried into it in 
suspension or mechanical admixture. Occasionally also vege- 
table matter of a glutinous nature is held in solution in the 
feed-water, and, precipitated by heat or concentration, covers 
the heating-surfaces with a coating almost impermeable to heat 
and hence liable to cause an overheating that may be very 
dangerous to the structure. A powdery mineral deposit some- 
times met with is equally dangerous, and for the same reason. 
The animal and vegetable oils and greases carried over from the 
condenser or feed-water heater are also very likely to cause 



THE MANAGEMENT AND CARE OF BOILERS. 463 

trouble. Only mineral oils should be permitted to be thus in- 
troduced, and that in minimum quantity. Both the efficiency 
and the safety of the boiler are endangered by any of these de- 
posits. 

The amount of the foreign matter brought into the steam- 
boiler is often enormously great. A boiler of 100 horse-power 
uses, as an average, probably a ton and a half of water per 
hour, or not far from 400 tons (406 tonnes) per month, steaming 
ten hours per day, and, even with water as pure as the Croton 
at New York, receives 90 pounds (41 kgs.) of mineral matter, 
and from many spring waters a ton (1.016 tonnes), which must 
be either blown out or deposited. These impurities are usu- 
ally either calcium carbonate or calcium sulphate, or a mixture; 
the first is most common on land, the second at sea. Organic 
matters often harden these mineral scales, and make them more 
difficult of removal. 

The only positive and certain remedy for incrustation and 
sediment once deposited is periodical removal by mechanical 
means, at sufficiently frequent intervals to insure, against injury 
by too great accumulation. Between times, some good may 
be done by special expedients suited to the- individual case. 
No one process and no one antidote will suffice for all cases. 

Where carbonate of lime exists, sal-ammoniac may be used 
as a preventive of incrustation, a double decomposition occur- 
ring, resulting in the production of ammonium carbonate and 
calcium chloride — both of which are soluble, and the first of 
which is volatile. The bicarbonate may be in part precipitated 
before use by heating to the boiling-point, and thus breaking 
up the salt and precipitating the insoluble carbonate. Solu- 
tions of caustic lime and metallic zinc act in the same manner. 
Waters containing tannic acid and the acid juices of oak, su- 
mach, logwood, hemlock, and other woods, are sometimes em- 
ployed, but are apt to injure the iron of the boiler, as may acetic 
or other acid contained in the various saccharine matters often 
introduced into the boiler to prevent scale, and which also 
make the lime-sulphate scale more troublesome than when clean. 
Organic matters should never be used. 

The sulphate scale is sometimes attacked by the carbonate 



4^4 THE STEAM-BOILER. 

of soda, the products being a soluble sodium sulphate and a 
pulverulent insoluble calcium carbonate, which settles to the 
bottom like other sediments and is easily washed off the heat- 
ing-surfaces. Barium chloride acts similarly, producing barium 
sulphate and calcium chloride. All the alkalies are used at 
times to reduce incrustations of calcium sulphate, as is pure 
crude petroleum, the tannate of soda, and other chemicals. 

Marine boilers have been effectively treated for the preven- 
tion or the removal of scale, by introducing sheet-zinc, or zinc 
in balls or in blocks of any convenient size and form. The in- 
crustation met with in marine boilers, properly managed, being 
always nearly pure sulphate of lime, the zinc, probably by some 
voltaic action, causes the deposit to become pulverulent, in- 
stead of compact, and very hard and strong, as when formed in 
the unprotected boiler, and it also compels the precipitation of 
the mineral upon the zinc itself principally. The water in boil- 
ers of any kind is very liable at times to become acidified per- 
ceptibly by the decomposition of the lubricants entering with 
the feed-water from the engine cylinders and condensers, and 
corrosion is thus accelerated. In such cases the zinc suffers 
and the boiler is preserved, if metallic contact is secured be-' 
tween the iron or steel and the zinc — precisely as, when the 
boiler itself is constructed of different qualities of metal, one 
part is preserved while another part is corroded. Zinc, as, 
relatively, an electro-positive metal, protects iron ; which latter 
is electro-negative to the former, and takes the hydrogen of so 
much water as may be decomposed by the voltaic action occur- 
ring, the zinc being attacked by the oxygen set free on that 
element of the voltaic pile so formed. Marine boilers thus 
protected have shown no trace of decay after years of use. 

Whenever zinc is used, the precaution should be taken to 
secure a perfect metallic connection between it and the boiler ; 
otherwise it will be neither uniform in action nor reliable. The 
zinc is sometimes amalgamated to prevent wasteful oxidation by 
local action. 

A little soda, or sodium carbonate, introduced into the 
boiler may often insure the formation of a softer deposit where 
it is found to be hard, and to so incrust and embalm the zinc 



THE MANAGEMENT AND CARE OF BOILERS. 465 

that it ceases to do its work. A surface of zinc of 25 to 50 
square inches (2.5 to 4.5 square decimetres, nearly) per ton of 
water contained in the boiler, and per month, is usually found 
ample. 

After studying the use of zinc as an " anti-incrustator," and 
the reports of M. Lesueur, who first introduced it extensively 
in France,"^ M. Euvrard concludes that it should be used in the 
form of " pigs" or ingots, and in any type or in any part of a 
boiler, although it is better not to place it on the heating-sur- 
faces of the firebox. He advises from one pound to two pounds 
for every ten square feet of heating-surface at a time {^\ to i 
kg. per sq. m.). It is found that zinc is valuable with calcareous 
feed-waters when not excessively hard, causing the deposit to 
become pulverulent, and thus altering an incrustation or scale 
into a sediment. 

Watcr-tiibc Boilers have been successfully treated by M. 
C. Quehaut,t where the incrustation was calcareous, and largely 
consisting of calcic sulphate, by using instead of the " tartri- 
fuges" commonly employed for such cases, none of which 
proved satisfactory, sheet-zinc of thickness No. 18. Sheet? 
about two metres (6.56 feet) long and 0.8 metre (3 feet) wide 
were cut into strips each about -^^ metre (3.28 inches) wide, 
and wrapped helically on a mandril, forming coils of which 
about 45 kilograms (100 pounds) were introduced into a boiler 
rated at 40 horse-power at each charge. The making of the 
coils cost about one dollar. One of the strips so coiled was 
pushed into each tube after each cleaning, and withdrawn at 
the succeeding period of washing out. Heavier zinc did not 
answer as well, as the strips were liable to be displaced by the 
circulating current. 

Incrustation takes place on the zinc instead of upon the 
adjacent iron surfaces. It is pulverulent, and easily removed. 
The cost was $2.50 per annum per horse-power. 

231. Repairs are the source of the great expense of main- 
tenance of steam-boilers, and sometimes of new dangers hardly 
less serious than those which they are expected to prevent. 

* Annales des Mines, 1877; Jour. Franklin Inst. 1S7S. 
f Ann, de I'Association des Ingenieurs de Liege, 4me serie, t. v., 1S86. 
30 



4^6 THE STEAM-BOILER, 

Frequent and systematic inspection and test will always reveal 
the approaching necessity of repairs long before serious risks 
are run, and, if promptly attended to and skilfully performed, 
the life of the boiler may often be very greatly prolonged. At 
sea it is customary to have on hand a good stock of extra 
boiler-plate, rivets, tubes, and other material for use in making 
repairs, and to have all minor and temporary repairs made by the 
engineer's crew. On land this is rarely necessary, as boiler- 
makers are usually close at hand, and the work can be done 
more perfectly, quickly, and cheaply by regularly employed 
workmen. 

Leaky tubes are often plugged until it becomes convenient 
to replace them by new ones. In such cases wooden or iron 
plugs are driven into the ends, and leakage thus checked. 
Sometimes special apparatus, devised with a view to con- 
venience of application while steam is still kept on, are em- 
ployed. Local defects, as oxidation or blisters, are remedied 
by bolting on " soft-patches" of boiler-plate fitted to the weak- 
ened surface and made tight by a cement of red-lead and oil, 
or a mixture of red and white lead and oil, with iron borings 
and some other constituent, as sal-ammoniac, the effect of which 
is to promote the oxidation of the borings and the production 
of a hard, stone-like cement. A permanent '^ job" is made by 
cutting out the defective metal, and riveting in a piece of new 
boiler-plate, thus making a '' hard-patch." A patch secured by 
tap-bolts is also sometimes called a '' hard-patch." 

Leaks in steam-pipes are stopped by placing sheet-rubber 
packing over the crack or joint, covering this with sheet copper 
or brass, and wrapping with tightly wound wire or cord. Feed- 
pipes may be similarly temporarily repaired, or by covering the 
leak with a " putty" of red and white lead and wrapping it with 
canvas and twine. 

Where a crack appears in any part of the heating-surface, if 
not more than two or three inches long, it should be stopped 
by drilling at each end and inserting a screw-plug. A long 
crack must be patched. Hard-patches are used when in con- 
tact with the fire ; soft-patches elsewhere : 

232. Inspection and Tests of strength should be occa- 



THE MANAGEMENT AND CARE OF BOILERS. 467 

sionally resorted to for the purpose of determining the precise 
condition of the boiler at the time, and its absolute safety under 
the .conditions of its regular use. Custom and opinion differ 
somewhat, among the ablest and most experienced engineers, 
as to the precise method and the extent to which such exami- 
nations and tests should be carried. It may be safely assumed, 
however, that the following principles and processes will be 
considered as, at least, on the safe side. 

The complete visual inspection and examination of a boiler, 
inside and out, should be considered one of the primary duties 
of the person responsible for its safe operation at every avail- 
able opportunity, and during its operation a watchful eye 
should be kept upon it uninterruptedly. With marine boilers, 
a complete examination is expected to be made every time that 
steam is off — usually at the end of every trip ; stationary and 
locomotive boilers are inspected at regular intervals by skilled 
inspectors or by the master-mechanic having charge of them. 
The former should be so examined at least once in each three 
months, and a complete inspection and thorough test should 
be made as often as once a year ; the latter still oftener de- 
mands attention. 

In a careful inspection, the inspector goes underneath and 
examines all the fire-sheets, and inside and with hammer and 
chisel and lamp examines every portion of the boiler. If a 
corroded or grooved place is found,, or a blister, it receives care- 
ful attention. If for any reason the examination should be 
made more complete, the hydrostatic test is applied. In the 
course of the examination, the safety-valves, the gauge-cocks, 
water-gauges, feed and stop valves, pumps, dampers, every de- 
tail, should receive careful attention. The tap of the hammer 
will, to the experienced ear — and inspection should only be 
intrusted to experienced men — reveal the thickness of a sheet, 
the presence of a crack, groove, or any form of serious oxida- 
tion or injury, the soundness of stays and braces and their con- 
nections, and the nature and extent of any defect that may 
exist. After this inspection the defects, if any, are removed, 
and after the repairs are completed the inspection should be 
repeated to make sure that the work has all been done, and 



4^8 THE STEAM-BOILER. 

properly done. Finally, the boiler is closed, filled to the safety- 
valve, all stop-valves being closed, and is subjected to a pres- 
sure exceeding its working pressure by at least one half, and 
preferably more. Many authorities advise a double pressure. 
While this operation is going on, the inspector carefully 
watches to see that no new weakness is revealed. 

That testing by hydrauHc pressure is not alone sufficient to 
reveal dangerous defects or to insure against disaster is un- 
questionable. The Author has repeatedly met with evidence 
that explosions have occurred at pressures less than those at 
which tests had been made ; and it is well known to experienced 
engineers, and especially to inspectors, that a dangerously thin 
boiler may sustain high pressures for a time. A case is related * 
in which a water-pressure of I2 atmospheres was sustained by a 
boiler which in places was exceedingly thin, and, as reported, 
at several points not thicker than paper. It not infrequently 
occurs that the inspector's hammer is driven through sheets by 
which very considerable pressures had been sustained. 

It was at one time common to test boilers to three times 
their working pressure, or even more ; but it is less usual now.. 
The United States regulations controlling steam-vessels pre- 
scribe a ratio of i-J- to i ; French regulations direct that a ratio 
of 2 to I shall be adopted for new boilers, annually, on naval 
vessels, and the same on merchant vessels at first, but later re- 
duced the ratio to i^- to i, although even then this pressure 
must not be kept up more than five minutes.f The British 
regulations prescribe 2 to i, the tests to be made semi annual- 
ly. If signs ojf weakness are observed the pressure may be re- 
duced. All boilers should be drilled occasionally wherever 
thinness of plate is suspected. All such tests and inspections 
should be made before painting, and inspection should be m^de 
while the boiler is still under the test-pressure. Leaks are 
often more easily detected under cold water than under steam- 
pressure , and the inspection rather than the test is the insur- 
ance against accident. This inspection and the hammer-test 
are especially relied upon where the boiler is one with the his- 

* Locomotive , Sept. 1873, P- 3' 

f Ledieu, Appareils a Vapeur, vol. ii. 



THE MANAGEMENT AND CARE OF BOILERS, 469 

tory of which the inspector is unfamiliar, and when old and 
worn ; as it is only by this plan that cracks, leaks, blisters, dis- 
tortion of parts, and corrosion can be satisfactorily found and 
gauged. 

All boilers are usually very carefully inspected inside and 
out at least once a year, and thoroughly tested. It is custom- 
ary to make quarterly examinations also as complete as possi- 
ble, but not, as a rule, to make the extended inspection and 
test which is insisted upon at the annual inspection. Where 
the feed-water is impure, however, and where sediment and in- 
crustation are found to give occasion, these periodical examina- 
tions should be made so frequently that all possible danger may 
be avoided. Every boiler should be cleaned out and thor- 
oughly freed from incrustation at intervals — whether a year, a 
month, or a week — such as will secure immunity from danger 
of overheating and from serious loss of economy. 

233. General Instructions for the management and care of 
boilers should always be written out and placed in the hands 
of attendants whenever they are not known to be in every re- 
spect familiar with their duties. Especially should they be 
cautioned against raising steam too rapidly, or emptying the 
boiler while the setting is hot, and against pumping cold water 
in large quantities into a hot boiler, and other errors of either 
omission or commission by which the boilers may be injured. 
All air-leaks about the setting should be found and stopped. 
The most perfect cleanliness should be enjoined. 

The most complete codes of instructions are those issued to 
naval officers, of one of which the following is an abstract : " 

The engineer officers are to make themselves acquainted 
with the general construction and with any special fitting of the 
boilers under their care. In order to protect the plates and 
stays from corrosion, it is essential that the interior surfaces 
should be coated with some impervious substance. A thin 
layer of hard scale, deposited by working the boilers with sea- 
water, has been found to be the most effectual preservative ; 
and therefore all boilers when new, or at any time w4ien any of 

* London Engineering, 1884. 



THE STEAM-BOILER 



the plates or stays are bare, are to be worked for a short time 
with the water at a density of about tJiree times that of sea- 
water, until a slight protective scale has been deposited ; but 
in this case care is to be taken not to allow a scale to be formed 
of such a thickness as would in an appreciable degree impair 
the efficiency and economy of the boilers. During the first 
six months' service the boilers should be frequently examined ; 
and afterwards, where possible, at least once a month, or after 
steaming twelve days. The boilers are to be examined care- 
fully after steaming ; and every judicious measure is to be used 
for the prevention and removal of scale, especially on the fur- 
nace crowns and sides. Whenever serious corrosive action has 
been discovered it is to be at once reported, together with full 
information as to the circumstances and the supposed cause. 
The tubes and tube-plates are to be cleaned as soon as possible 
after steaming. 

It is essential that at first the water should be kept for a 
short time at about three times the density of sea-water, until 
the thin protective scale has been formed, as before directed. 
After this, in the ordinary working of the boilers, the engineer 
officers in charge of machinery are to use their discretion as to 
the most suitable density at which the water in the boilers 
should be kept for the service on which the ship is employed. 
This density, which is in no case to exceed three times, nor be 
less than one and a half times that of sea-water, will probably 
vary to some extent, on different stations and under different 
conditions of working, of regular service, and the engineer offi- 
cers will be guided in their selection of the working density by 
their experience of the economy of fuel under steam, and of 
the state of the boilers after steaming. No tallow or oil of ani- 
mal or vegetable origin is to be put into the boilers to prevent 
priming, nor for any other purpose whatever. 

When the boilers are empty, the fires are not to be kept 
laid ; the boilers are to be kept dry and warm ; all accessible 
parts are to be frequently examined and cleaned ; and the 
lower parts are to be coated with red and white lead, or other 
protecting substance. Where the boilers cannot be kept thor- 



THE MANAGEMENT AND CARE OF BOILERS. 



471 



ongJily dry and warm, they are. at the discretion of the engineer 
officer in charge, to be kept quite full. "^ 

The boilers should not be exposed to sudden changes of 
temperature ; the steam should not be raised rapidly ; the 
smokebox doors should not be opened suddenly, as a rush of 
cold air through the tubes affects the ends — and the tubes 
leak ; and the stop and safety valves should be opened grad- 
ually. The safety-valves should be partially raised each watch 
to test the fittings, and the smokebox doors should not be 
opened except when absolutely necessary. The blow-off cocks 
are to be kept in good condition. 

The spaces at the backs and sides of the boilers are at all 
times to be kept clear ; and on no account is anything combus- 
tible to be placed on the top of the boilers or in contact with 
them. Every care is to be taken to prevent any accumulation 
of soot or coal-dust between the uptake and casings of the boil- 
ers, and, when necessary, means should be provided for exam- 
ining the air-space between the uptake and the air-casing, and 
every possible precaution taken to prevent the clothing of the 
boilers being set on fire. 

It is well to keep a log in the boiler-room, where a large 
" plant" is operated, and the record so kept should exhibit all 
important data relating to its operation. The following is a 
good form of ruling for the blanks or log-book employed : 



BOILER RECORD.— Week Ending. 



No. of 
Boiler. 


Average 
Pressure. 


Hours 
Steaming. 


Coal, 
Tons. 


Ashes 
Removed 


Water 
Used. 


Remarks. 
















Totals.. 















Memoranda.— 



* A small quantity of washing soda or other alkali may be introduced with ad- 
vantage. 



CHAPTER XIII. 

THE EFFICIENCIES OF STEAM-BOILERS. 

234. Steam-boiler Efficiency is not difficult of definition 
when the nature of the quantity to be measured is itself first 
understood. There are, however, as will be presently seen, 
several different efficiencies of the steam-boiler, as of the steam- 
engine ; and it is important that each be distinctly defined be- 
fore a study of either, or of total efficiency, can be made. In 
general, it may be said that efficiency is measured by the ratio, 
in common or similar and definitely related terms, of a result 
produced to the cost of its production. As, in the study of 
the steam-engine, either efficiency is measured by the ratio of 
work done in the specified manner to the work or work-equiva- 
lent expended in doing it ; so, in the case of the steam-boiler, 
either efficiency is measured by the ratio of a heat-effect, or its, 
equivalent, to the quantity of heat, actual or latent, paid for 
its accomplishment. 

In some cases it is not practicable to thus establish a nu- 
merical value of an efficiency ; and it can only be shown that 
efficiency, in the sense of quantity of result compared with 
magnitude of means used, is increased or decreased by the op- 
eration of defined phenomena, or by conditions which can be 
specified. A common measure cannot always be found, or an 
exact law of relation established. 

Increasing steam-pressure gives increasing economy up to a 
limit somewhere above customary pressures. The higher the 
pressure the greater the economic value of the steam in a 
steam-engine, but on the other hand the lower the efficiency 
of the boiler ; and it is perfectly possible to reach a point at 
which the gain on the first score is more than counterbalanced 
by the loss on the second. Where the object sought is simply 
heating-power, the advantage lies, on the whole, on the side of 
low pressures. 



THE EFFICIENCIES OF STEAM-BOILERS. 4/3 

235. The Measure of Efficiency of boilers is commonly a 
ratio of heat applied to a defined purpose or obtained in store, 
in a stated form, to the total quantity of heat from which it 
has been saved, another part having been diverted to other 
purposes, and, for the use considered, wasted. Thus, a given 
quantity of heat being stored as potential energy of chemical 
action in fuel, a small proportion of that energy is received at 
the steam-engine when that fuel is burned under a steam-boiler ; 
the ratio of these two quantities — always a fraction and often 
small— is the total efificiency of the whole apparatus employed 
in the combustion of fuel, the transfer of heat-energy to the 
fluid in which it is stored, and its further transfer to the point 
at which it is usefully applied by transformation into mechani- 
cal energy and work. 

236. The Efficiency of Combustion thus measures the 
ratio of the available heat-energy of the fuel to that set free by 
its union with oxygen, and is less than unity in the proportion 
in which the combustible portion of the fuel escapes such 
chemical change or is imperfectly burned, as when a part of the 
fuel falls into the ash-pit, is imbedded in clinker, or remains 
on the grate when the fire is extinguished ; or as when carbon 
is only oxidized to carbon monoxide instead of being com- 
pletely burned into dioxide. In well-managed furnaces the 
value of this efficiency approaches unity ; it ought not to fall 
below 0.90, probably, in any ordinary case. 

237. The Efficiency of Transfer of Heat similarly meas- 
ures the ratio of heat received from the furnace by the boiler 
to that produced by combustion. That not transferred to the 
boiler is either sent up the chimney, where it is, in a certain 
degree, useful in producing draught, or it is lost by conduction 
and radiation to surrounding bodies. In good examples, the 
value of this ratio exceeds 0.75, and it should not usually fall 
under fifty or sixty per cent. Its best value depends on con^ 
siderations, however, to be hereafter stated, and it is not al- 
ways desirable that it should have the highest value possible, 
or approximate unity. 

238. The Net Efficiency of Boiler is the continued prod- 
uct of all efficiencies of the several operations constituting the 



474 THE STEAM-BOILER. 

process of production and supply of steam ; and it can only be 
exactly known by direct experimental determination, either as 
a whole, or in detail, by the ascertainment of the values of 
each of its factors. It is this quantity with which the engineer 
and the proprietor are principally concerned, and the study of 
the elementary efficiencies is mainly useful in revealing the 
causes and the extent of wastes in the several steps of the 
whole process. 

239. The Finance of Efficiency is a more important mat- 
ter, if possible, than the theory of either or all the efficiencies 
already defined. It is obvious that, in any case in which steam 
is demanded at a given pressure and in stated quantity, it may 
be obtained either expensively by using ill-chosen types, con- 
struction, and proportion of boiler, and operating under un- 
fortunate conditions, or economically by an opposite method. 
In general, the larger the boiler the less the cost of steam in 
fuel and operating expenses ; the smaller the boiler the heavier 
the coal bills and related accounts. On the other hand, the 
larger boiler is of great first cost, expensive in its interest, in- 
surance, and perhaps maintenance, accounts ; while the oppo- 
site is true of the smaller boiler. It is equally evident that a 
boiler may be too large and costly for real and ultimate financial 
economy ; or it may be too small and too wasteful of fuel to give 
best results as read on the final balance-sheet, at the end of its 
period of service. There must in every case be some proportion 
of size and cost to quantity of steam demanded which shall, on 
the whole, prove in the end a financial success, and give the 
work required of it at the least total cost. 

240. Commercial Efficiency must thus be added as the 
final and most important of all efficiencies, as judged from the 
standpoint of the proprietor, and as measuring also the success 
of the designer of the steam-generating apparatus ; and the fol- 
lowing definitions and principles may be admitted as a basis 
for the mathematical theory of the finance of steam-boiler 
operation : 

In the design and construction of a steam-boiler, and in its 
operation, problems arise which must be solved by the mechan- 
ical engineer in their natural order before he can say with 



THE EFFICIENCIES OF STEAM-BOILERS. 475 

confidence that the best interests of the purchaser or proprietor 
of the apparatus are fully met in its construction and manage- 
ment. Such are the following : 

(i) The '' Efficiency of tJie Steam-boiler ' is the ratio of the 
total quantity of heat utilized in the production of steam to 
that set free in the combustion of the fuel. It has as the 
maximum limit unity, and is a function of area of heating-sur- 
face, and of factors dependent upon the character of the fuel 
and its combustion, and upon the design of the boiler. 

(2) The " Commercial Efficiency' or the " Efficiency of Capi- 
tal employed in the maintenance of steam-generating appa- 
ratus of a given power is measured by the ratio of quantity of 
steam produced to the total cost of its continuous production, 
i.e., by the reciprocal of the total cost of steam per pound or per 
cubic foot at the required pressure. This efificiency is a maximum 
when that cost is a minimum. 

(3) TJie '^Efficiency of a Given Boiler Plant,'' as the Author 
has called it, or the commercial efficiency of a steam-boiler 
already in place and in operation, is still another quantity. It 
is a maximum when the work done by the boiler can be in- 
creased beyond that for which it w^as proportioned — if de- 
signed originally to give maximum efficiency of capital at a pre- 
arranged power, as above — until the amount of steam made by 
that h6\\^x per dollar of working expense is made a maximum. 

These three efficiencies differ essentially in their character, 
and are determined by different processes. In the first case, the 
engineer designing a boiler finds himself called upon to deter- 
mine what is the maximum efficiency that it will be economical, 
or otherwise advisable, to endeavor to secure, and then ca^ 
culates the proportions necessary to secure that efficiency. 
Or, knowing the proportions of any boiler already designed and 
built, he may be required to calculate its probable efficiency 
and the quantity of fuel required to make a certain quantity of 
steam, i.e., to estimate the quantity of steam which will be 
generated per pound of coal burned. 

In the second case, the designing engineer calculates the 
proportions of heating-surface to grate-surface or to fuel 
burned, where the quantity of steam required is known, and the 



47^ THE STEAM-BOILER. 

conditions determining costs, which shall give that quantity of 
steam at least total running expense. The investigation de- 
termines how large a boiler or what extent of heating-surface 
will, all things considered, pay best. 

In the third case, the boiler is in place and in operation, and 
it is found that it is advisable to ascertain what quantity of 
steam is made when the cost of that steam, per unit of weight 
or of volume, becomes a minimum. 

In the first two cases, the variable element is usually the area 
of heating-surface per pound of fuel burned in the unit of time; 
in the last, the variable may be either the quantity of fuel 
burned or of steam made. 

(4) To what Capacity may any Given Boiler be forced with- 
oiLt exceeding that Cost of Steam at which a Paying Profit is 
given ? is another problem in steam-boiler efficiency, and one 
which is of more frequent occurrence and is usually more im- 
portant than the preceding. 

The economical maximum of steam-production is evidently 
determined by the money value, to the producer, of the steam 
made. 

241. Efficiency of the Steam Boiler. — This case has been 
studied by Rankine, who deduces a very simple and handy 
formula for the efficiency of a boiler of known proportions, 
using a fuel of known calorific value. 

Taking the rate of conduction of heating-surfaces as varying 
as the square of the difference of temperatures of the gas and 
of the water on opposite sides of the sheet, the formula 

£= i 

is readily deduced, in which E is the efficiency, a a constant, d 
the specific heat of the furnace-gases, and W their weight'; 
while H is the total heat expended and 5 the heating-surface. 
This expression is further transformed into 

BE 



E. ^ 






THE EFFICIENCIES OF STEAM-BOILERS. A77 

in which E is the theoretical evaporative power of the fuel per 
pound, E, the probable actual evaporation in a boiler in which 
F is the weight of fuel burned on the unit of area of grate, and 
5 is'the area of heating-surface per unit of the same area. 

A and B are here coefficients, having values respectively of 
0.3 to 0.5 and 0.9 to i for bituminous coals, according to Ran- 
kine, and from 0.3 to 0.5 and from 0.8 to 0.9 with anthracite 
coal, as determined by experiments made by the Author. The 
lowest and best values of A are obtained when using a minimum 
needed air-supply, and the value of that coefficient is seen, by 
comparing the two equations just given, to vary as the square 
of the quantity of air supplied to the fuel. The value of B is 
dependent upon the character of the boiler, being greater as 
the design and construction are improved. 

The following are illustrations of the results thus obtained : 
Efficiency of Steam-boilers. 
I. II. III. IV. 

^ = 0.3;^=!. ^=0.5;^=!. A= 0.3; B=i. 

0.95 0.83 0.86 

0.91 0.78 0.82 

0.89 0.75 0.80 

0.87 0.72 0.78 

0.83 0.68 0.75 

242. Commercial Efficiency of the Boiler.— The expenses 
of operating a steam-boiler may be classed under three heads : 

(i) Those costs of boiler and its maintenance which are de- 
pendent upon the size and the character of the boiler itself and 
its attachments, such as interest on cost of boiler and setting, 
rent of building, and other items on construction account, such 
as taxes, insurance, repairs and depreciation, etc., etc. 

(2) Those costs of operation which are dependent upon the 
quantity of steam made and of fuel consumed, such as market 
price of fuel, cost of transportation, storage (an important item 
on shipboard especially), and of feeding into the furnace, cost 
of feed-water and its introduction into the boiler, and often a 
certain part of other costs of attendance and supply. 

(3) In addition to these variable expenses are often, perhaps 
usually, to be counted certain constant expenses which are un- 



f- 


= 0.5; ^ 


0.17 


0.92 


0.33 


0.87 


0.40 


0.83 


0.50 


0.80 


0.67 


0.75 



478 



THE STEAM-BOILER. 



affected by any change of proportions of boiler likely to be 
made in the assumed case, such as nearly all, or frequently quite 
all, the costs of attendance. 

A given amount of steam being demanded, it may be ob- 
tained either from a boiler so small as to use fuel extravagantly, 
or from a large boiler using fuel economically. In each case 
arising in practice, there will be found a certain easily deter- 
mined proportion of heating-surface to grate-surface, and a 
definite size of boiler which will, on the whole, supply the de- 
sired quantity of steam most economically. Thus: 

Let the total cost of fuel per annum and per pound burned 

per hour on the square foot of grate or on the square metre be 

called C. Let the total cost per annum of boiler, per square 

foot or per square metre of heating-surface, be called D^ and let 

C 

— znzR, In the first item is included Class i, and in the second 

Class 2. 

Then the cost of boiler maintenance per annum is DSG, 
where 5 is the area of heating-surface per unit of area of grate 
and G is the area of grate. The cost of fuel, etc., per annum, 
as per Class 2, is CFG, if F is the weight of fuel burned per 
unit of area of grate. 

The total of costs variable with change of proportion of 
boiler is 

P = DSG + CFG. 

The profitable work of the boiler is measured by the quantity, 
by weight, of steam made, FGE^^= W\ E^ being the evapora- 
tion of water per unit of weight of fuel. 
The ratio of cost to work done is 

P_ _ DGS + CFG _ CF+DS 
W~ 



y 



FGE. 



E.F 



This quantity being made a minimum by variation of the 
area 5, the most economical boiler is obtained. 

But E^ is a function of 5, and, taking the value of E^ from 
the equation 



1 + 



S 



THE EFFICIENCIES OF STEAM-BOILERS. 



479 



we obtain 



{pGS-\-CFG)[i-^'^^ DGS + ADFG + CFG^ 



ACF'G 



S 



y- 



BEFG 



BEFG 
DS + ADF-\-CF + 



ACF' 
S 



which is a minimum when 



' D F 



BEF 



-^ S. ,-r-. 



^/AR. 



In illustration : Let a boiler, set in place, complete with all 
its appurtenances and in running order, cost $3 per square foot 
of heating-surface, and the annual charges on all accounts en- 
tered in Class i, above, be 20 per cent on this cost, the annual 
charge becomes DS = $0.60 X vS per square foot of grate, i.e., 
D = $0.60. Let the cost of operation, as for Class 2, amount 
to $15 per annum per pound of fuel burned per hour on the 

C 



square foot of grate ; then CF— $15 X i^; C 



^S:^ = R 



25. 



Assume F= 10 pounds of fuel per hour per square foot of 
grate, A =0.5. 

For this case, then, the boiler should have per square foot 
of grate, 

S, = FVAR= 10 x{o.SX2S)i = 3S; 
35 square feet of heating-surface. 

Similarly we get the following values : 

Commercial Efficiency of Boilers. 

Ratio of Areas of Heating and Grate Surfaces. 

Values of S. 



F 


6 


10 


12 


^5 


20 


30 


40 


50 


R 


















25 


21 


35 


42 


52 


70 


105 


140 


175 


16 


17 


28 


34 


42 


56 


84 


112 


140 


9 


12 


21 


24 


32 


42 


63 


84 


105 


4 


8 


14 


16 


21 


28 


42 


56 


70 



480 THE STEAM-BOILER. 

These values are 20 or 25 per cent lower for forced draught. 

Where the boiler is worked almost continuously, as in flour- 
mills and some other establishments kept in operation night 
and day throughout the year, the higher values will be found 
correct ; when the boiler is w^orked discontinuously or, as in 
steam fire-engines and some classes of steam-vessels, a com- 
paratively small proportion of the annual working time of the 
establishment or whole plant, the values of 5^ become very 
small. 

It is seen that the best area of heating-surface will vary 
nearly as the square root of the total working time per annum. 
Boilers worked continuously, worked twelve hours out of the 
twenty-four, and eight hours in the day, will require, respective- 
ly, values of 5 having the proportion i, 0.7, and 0.6 nearly. 

W 
The total required area of grate is -^-^ = G\ the total area 

of heatmg-surface is -^^y^- == 0),6r =: -wwh 

The following are examples, in greater detail, of the appli- 
cation of the above : 
Expense on Boiler Account and Maximum Commercial Efficiency. 

Cases. Staiionary. Marine. 

I. II. III. IV. 

Class I {D) Cornish. Tubular. Tubular. Tubular. 

Total annual cost of boiler per unit of S.. .. . $1.50 $2.00 $3.00 $2.00 

Interest .09 .12 .15 .12 

Repairs and depreciation 15 .20 .45 .30 

Rent, insurance, and miscellaneous .to .07 i.oo .20 

Total value of Z) 34 .38 1.60 .62 

Class 2 (C). 
Fuel (@ $5 for I., II., IV.; $4 for III.) per unit 

oi F 7.50 7.20 12.00 2.00 

Transportation and storage r.oo i.oo 10.00 i.oo 

Attendance (variable cost) 0.00 0.50 0.50 0.00 

Total 8.50 9.00 22.50 3.00 

C 
Value of— =i? 25 23 14 5 

Value of ^ 0.5 0.3 0.3 0.5 

Value of |/^ 3-5 2.7 2.0 1.6 

Value of i^ 8 10 16 20 

Value of \/'AIi = Si 28 27 32 32 



THE EFFICIENCIES OF STEAM-BOILERS. 48 1 

R varies in magnitude very greatly in practice, falling as low 
as 4 and rising as high as 50 with varying cost of fuel and 
length of working time. 

The engineer thus solves this important problem in boiler- 
design which may be thus enunciated : To determine the com- 
mercial efficiency of a steam-boiler doing a fixed amount of 
work ; or, given all variable expenses of boiler installation,, 
maintenance, and operation, to determine what proportion of 
heating-surface to grate-surface, or to fuel burned, will give the 
required amount of power at least total cost. 

243. Commercial Efficiency of a Fixed Plant.— A 
second commercial problem may sometimes be presented to the 
engineer : A steam-boiler is in place and in operation ; all con- 
stant expenses are known and all variable costs of mainten- 
ance and operation are determinable. The question arises, 
or may arise whenever additional steam may be usefully 
employed : How much work can be obtained from the ap- 
paratus when driven to such an extent as to yield the maximum 
amount of steam per dollar of total cost of operation ? The 
independent variable is now the quantity of fuel burned in the 
boiler, and this is, in the established equation, represented by 
F, the fuel burned per unit of area of grate. This problem is 
thus stated : 

Given : All expenses, constant and variable, the method 
of variation of the latter, and the proportions of the boiler 
being given, to determine that rate of combustion which will 
make the commercial efficiency of the given plant a maximum. 

For this case let K represent that total annual expense of 
working which is independent of Classes i and 2 and which falls. 

into Class ^, and let k =^ -^. 

Let all other symbols stand as before. 

Then the total cost of maintenance and operation will be 

F ^kGArDGS+CFG, 

while the work done will be, as before. 



W^FGE,. 



31 



4^2 THE STEAM-BOILER. 

The quantity to be made a minimum is, for the present case, 
the quotient of P' by W, 

_P' _ k-\-DS+ CF 
^^~ V/- E,F ~ ' 

/^ being taken as the independent variable. 

This becomes a minimum when we substitute for E^ its value 

BE 
E^ = ^-7,, and make the first derivative equal zero. 



'+ s 

Then we find 



.^^kSA-BS' 



AC 



When, in this expression for the value of F, giving maxi- 
mum weight of steam for the dollar expended, we make /^ = o, 
the expression maybe reduced, as obviously should be possible, 
to the form shown already to be that giving the solution of 
the first problem : 

S, = FVAR, 
The following cases illustrate this problem : 

Expenses of Boiler and Maximum Economy of Plant. 

Cases. Stationary. Marine. 

I. II. III. IV. 

Cost of maintenance : i? ,. , $0.34 $0.58 $0.88 $0.62 

Cost of operation : C. , 8.20 9.00 14.50 3.00 

Cost of operation : K. 30.00 25.00 10.50 10.00 

For maximum fuel and work : 7^1 16 13 17 21 

For maximum efficiency, as before : F 8 10 16 20 

Case No. i is that of a Cornish boiler, No. 2 that of a mul- 
titubular stationary boiler. No. 3 that of a sea-going steamer, 
and No. 4 that of a yacht. 

It is seen that in all cases the weight of steam delivered from 
the boiler and the quantity of fuel burned at maximum com- 
mercial efficiency, for the case assumed, are less than where the 
boiler- -once set and still capable of being forced to deliver 



THE EFFICIENCIES OF STEAM-BOILERS. 483 

more steam than originally proposed and calculated upon — is 
worked up to a maximum delivery per dollar of total expense. 

"Maximum commercial efficiency of boiler" and "Maxi- 
mum efficiency of a given plant " are therefore by no means 
identical conditions ; and it will usually be found that when this 
maximum work can be put on the boiler, it might be done still 
more economically by a boiler specially designed, as in the first 
problem, to do the increased quantity of work : the conclusion 
from this fact being simply that economy dictates that as much 
steam-power as possible should be grouped into a single plant 
in order to diminish the proportional cost of the constant part 
of running expenses, i.e., otherwise stated, there being given a 
certain necessary expenditure, invariable within certain limits 
with variation of size of boiler or of quantity of steam made, 
the larger the amount of work done without increasing this 
constant expense, the cheaper will the steam be made. 

The larger the plant supervised by the engineer the less the 
total cost per pound of steam made, other conditions of econ- 
omy being unchanged. 



CHAPTER XIV. 

STEAM-BOILER TRIALS. 

244. Th« Object of a Trial of a Steam-boiler is to de- 
termine what is the quantity of steam that a boiler can supply 
under definitely prescribed conditions ; what is the quality, as 
to moisture or dryness, of that steam ; what is the amount of 
fuel demanded to produce that steam ; what the character of 
the combustion, and the actual conditions of operation of the 
boiler when at work. The conditions prescribed for one trial 
may differ greatly from those of another trial, and such differ- 
ences are often the essential matters to be studied. In any 
case it is assumed that the conditions under which the boiler is 
to be worked are to be definitely stated, and the engineer con- 
ducting the experiments is expected to ascertain all the facts 
which go to determine the performance of the boiler, and to* 
state them with accuracy, conciseness, and completeness. 

In the attempt to ascertain those facts the engineer meets 
with some difficulties, and finds it necessary to exercise the 
utmost care and skill. In conducting a steam-boiler trial the 
weight of the water supplied to the boiler must be determined ; 
the weight of the fuel consumed must be obtained ; the state 
of the steam made must be determined ; and these quantities 
must all be noted at frequent intervals. It is also necessary to 
know whether the combustion is perfect or imperfect, and to 
what extent the conditions and facts noted are due to the 
boiler, and what to external conditions. 

It has now come to be considered that the determination of 
power and economy of a steam-boiler demands all the care, skill, 
and perfection of method and of apparatus of any purely scien- 
tific investigation. It is essential that all work of this kind shall 
be done in substantially the same way, in order that compari- 
sons may be made. 



STEAM-BOILER TRIALS. 485 

245. Tests of Value of Fuel are sometimes the sole object 
of a trial of a steam-boiler, the intent being to ascertain by 
actual experiment what quantity of water a fuel of unknown 
quality can evaporate in a boiler of which the general ef^ciency 
is fairly well established. In such cases the fuel is employed 
in the usual manner and the results compared with those ob- 
tained with fuels of known excellence. Thus, in a good type of 
boiler, having a good proportion of area of heating-surface to 
weight of fuel burned per hour, it may be found that a fuel of 
established reputation for uniform excellence will evaporate ten 
times its own weight of water " from and at " the boiling-point. 
The trial of a fuel of unknown quality may prove that this 
boiler will, under precisely similar conditions, evaporate an 
equal amount of water into steam, and yet the market price of 
the fuel may be considerably less than that of the other. 
The immediate result would be the substitution of the second 
for the first, should no counterbalancing disadvantages exist. 
In such cases the method of conducting the experiment is 
precisely the same as where the efificiency of the boiler is de- 
termined ; but the object sought is quite a different one. This 
also commonly compels at least two trials, the one of the 
old and standard, the other of the new and uncertain fuel, and 
a comparison of boiler-efficiency as found in the two trials. 

246. The Determination of the Value of a steam-boiler 
involves the measurement of its efficiency, independently of the 
nature of the fuel, and it is thus important that a standard 
system of measuring the effectiveness of the fuel should be 
settled upon, or that all variations of such effectiveness should 
be eliminated. The latter is commonly the course taken ; and 
the determination of the efficiency of the boiler is based upon 
the measurement of the evaporation of water, under stated 
standard conditions, per unit weight of the combustible and 
burned portion of the fuel supplied during the trial. 

But the power of the boiler is as important an element of 
its value as its efficiency, and a complete trial includes, usually, 
measurements of efficiency at both the rated and the maximum 
working power of the boiler as operated for its special purpose. 

247. The Evaporative Power of Fuels depends upon 



486 THE STEAM-BOILER. 

not only their chemical composition as fuels, but also to an 
important extent upon their structure and their physical con- 
dition in every aspect ; on their greater or less purity, and the 
admixture of earths, moisture, or other foreign matters ; the 
fitness of the furnace for their utilization ; the air-supply ; its 
quantity, temperature, and humidity ; the proximity of chilling 
surfaces ; the extent of the combustion-chamber in which the 
gases rising from the bed of coal or other combustible may be 
more or less completely consumed ; and many other minor con- 
ditions, all of which tell, in a, more or less important degree, 
upon their value and the efficiency of the system of heat- 
generation. 

248. Analyses of Fuels are sometimes made, either as a 
check upon the results of the trial or in substitution for it. 
Should analysis show that a given fuel is rich in heat-producing 
elements, while trial fails to give the results that should have 
been obtained, and such as the use of other fuels in the same 
boilers indicates to be possible, it will at once appear that the fuel 
demands peculiar treatment, or some other arrangement of 
furnace. Should doubt exist which of a number of fuels of the 
same class is best, chemical analysis may give a quicker and 
cheaper answer to the question than a formal trial. It rarely 
happens, however, that any system is as satisfactory, in the end,, 
as actual trial extending over so long a period as to eliminate 
uncertainties. 

Methods of analysis differ somewhat. The following is a 
standard method of general treatment as prescribed by the 
Union of Engineers of Germany :* 

In order to take a sample of the fuel, a shovelful from 
each barrow or wagon will be thrown into a box with a cover. 
The coal will be mixed up and spread in the form of a square 
upon a level floor, and then divided by two diagonals into four 
parts. Of these, two opposite parts will be taken away, the 
other two will be broken up small and mixed together. Another 
shovelful will then be thrown in, and the method continued 
until about 10 kilogrammes are in the box. This will then be 

* American Engineer, August, 1883. 



STEAM-BOILER TRIALS. 48/ 

closed and reserved for chemical analysis. For accurate ex- 
periments the halves which have been taken away should also 
be analyzed. 

To determine the moisture in the coal, about 10 grammes 
from the above-named sample is to be heated for two hours to 
105° or 110° C. The loss in weight shows the moisture in the 
coal. Coal which happens to have been wetted by rain or 
otherwise should not be used. The test should be applied to 
coal in the average state of moisture at which it is delivered 
from the pit mouth, and this state should, if necessary, be 
determined beforehand. The remainder of the sample, pow- 
dered and mixed thoroughly, serves to determine the ash, the 
carbon, the hydrogen, the nitrogen, and the sulphur. The 
heating-value of the coal is determined as follows : Suppose 
that it is found to contain c per cent of carbon, h per cent of 
hydrogen, s per cent of sulphur, per cent of oxygen, and w 
per cent of water, then the theoretical heating-value is given 
by the formula of Dulong as follows : 

{a). Referred to Water at 0° Cent. 

8100^ + 3432^ r-^y + 250OJ. 

{b\ Referred to Water at 100° Cent. 

8100^+ 34200 \Ji — ^j -f 250OJ — 636.5 (9/2 + w.) 

To determine the quantity of air required for burning coal 
we have the following: One kilogramme of coal requires to 
burn it, 

2.66^c -f 8/^ + ^ - ^ 
1^0 X 1.43 ^^' "^^^^^^ ^^ oxygen ; or, 

2.667^ ^ Zh -^ s — 

cu. metres of air contammg 21 per ct. 



21 X 1.4^ r 

^^ 01 oxygen. 

The analyses should be made with care, by a skilled and 
experienced chemist, if any important question is to be settled. 

249. Economy of Fuel is nearly synonymous with effi- 
ciency of boiler, as a matter of engineering simply ; but when 
the finance of the case is studied, it is often found, from that 



4^8 THE STEAM-BOILER. 

point of view, a very different mattter. It is perfectly possible 
to adopt so great a proportion of heating-surface, so large a 
boiler, that the gain in fuel saved, as compared with boilers of 
similar type and usual proportions, may be more than offset 
by the increased charges on account of enlargement of boiler. 
The efficiency of boiler, in the ordinary sense in which that 
term is used, is, however, a measure of economy. The varia- 
tion of efficiency and of economy in fuel consumption is a func- 
tion of the proportion of area and of heating-surface to fuel 
burned, and the object of a boiler-trial is to ascertain these rela- 
tions with precision. An understanding should be had before 
the trial in regard to the kind of fuel to be used ; where no reason 
of controlling importance exists to the contrary, the best obtain- 
able coal should be selected, for the reason that a boiler can be 
better judged, and the results of its trial may be more satisfac- 
torily compared with similar trials of other boilers, when the 
very best work of which it is capable is done by it. The 
differences betw^een separate lots of the best coals are less 
than the differences between separate lots of inferior fuels, 
and the comparison is thus less difficult where the former are. 
used. 

The results of a boiler-trial at Cassel are reported to have 
given the following distribution of heat :'^ 

B. T. U. per cent. 

Heat of I lb. coal utilized 11.498. 4 80.34 

Carried off by gases 1.03T.4 7.21 

'* " brickwork 286.2 2.00 

" " ashes 2340 1.63 

*' " " radiation, etc.. 1,261.8 8.82 

14,311.8 100.00 

The coal contained : 

C 82.51 percent. 

H 4-73 " " 

4.68" " 

HoO 1.38 " " 

Ash and Waste 6.70" " 

100,00 
* Abstracts of Papers, XC, 1887, p. 70, Inst. C. E. 



STEAM-BOILER TRIALS. 489 

The data of the trial were : 

Steam pressure (atmos.) 6.36 

Water evap. per hr., lbs 4,501.79 

'* " " sq. ft. H. S. per hr., lbs 2.99 

" " " lb. coal, lbs 10,50 

Temp, feed-water in tank (Fahr.) 64°. 4 

" " " from heater 115°. 52 

" air in boiler-house 69°. 8 

" gas leaving flues 345°.2 

Ratio air to theoretical quantity ;... 1.31 

Coal per sq. ft, G. S. per hr., lbs 14-67 

" " " H. S. " " " 0.297 

250. The Relative Values of Boilers depend not only on 
their efficiencies, but also on their capacities for furnishing steam, 
and on various other qualities and attributes : as their greater 
or less complication in structure ; their safety and durability ; 
their volume, weight, and cost. The boiler-trial only settles 
questions relating to their efficiency and capacity, and their real 
relations of value, only just so far as those elements enter the 
problem. These are usually, however, the main factors, and 
their measurement by a test-trial gives the means of deciding, 
in nearly all cases, every question likely to present itself in the 
use of the apparatus. 

251. Variations of Efficiency occur with variations in 
grate-area, in rate of combustion and in kind of fuel. In 
any given boiler, within a wide range of which the limits are 
usually far outside of practical conditions, the greater the 
quantity of fuel burned the less the amount of steam made per 
unit weight of that fuel ; the smaller the quantity of fuel, 
burned under proper conditions, in the boiler, the higher the 
efficiency ; and it has been seen in an earlier chapter, that 
the gain in efficiency, Avith increasing proportion of heating to 
grate surface or to fuel burned, is less and less as this increase 
goes on. By enlarging or reducing the grate, or by increasing 
or diminishing the draught and air-supply, and during a suc- 
cession of trials, noting the method of variation of efficiency 
and of capacity for making steam, the law of such variations 



490 THE STEAM-BOILER. 

may be established, and the best arrangement, all things con- 
sidered, may be determined. 

252. Variations of Proportions in different boilers, other- 
wise similar, have been seen to be capable of expression by a 
very simple algebraic expresssion on which all theories of effi- 
ciency are based. But in some cases this law is not found to 
be precisely applicable, and only test-trials of boilers so 
differing can be relied upon to give correct relations. The 
general relations already stated invariably hold ; but it often 
happens that a steam-boiler exhibits peculiarities which make 
that exact statement inapplicable. It is not uncommon not 
only to compare actual performance, as shown by trial, with 
the results indicated by the theory, but also to alter the ratio 
of heating to grate surface by bricking over more or less of 
the grate, and by this or other expedients so varying that 
ratio in successive trials as to obtain an empirical and approxi- 
mately exact expression for the law of variation of efficiency 
for the particular case in hand. 

253. Combined Power and Efficiency distinguish the best 
types of boiler. That which, at a given cost, exhibits highest 
steam-producing power combined with greatest efficiency, is 
the best boiler. These qualities, however, are not usually com- 
patible, and increased steam-production from any boiler is com- 
monly attended with a decrease in efficiency; and as the one or 
the other of these qualities is the more important, the combi- 
nation which will give best total result will vary. In no two 
cases will the same combination be equally desirable. Every 
boiler must be tested for both before it can be said whether it 
is satisfactorily adapted to its place and work. 

254. The Apparatus and Methods of test-trials should be 
prescribed in the preliminary arrangements for every trial, and 
if possible should be in exact accordance with some accepted 
standard rules. The apparatus consists of scales and tanks for 
measurement of weights of coal and of water ; gauges to give 
the pressure of steam ; thermometers of great accuracy to 
determine the temperatures of water, steam, and flue-gases ; 
and calorimeters to determine the quality of the steam and 



STEAM-BOILER TRIALS. 49 1 

the extent of superheating, or the percentage of moisture en- 
trained by it. 

The estabhshment of the correctness of this apparatus is the 
first 'of the prehminaries to their use. The standardization 
of the instruments is a matter of supreme importance, since 
upon their accuracy the whole work of the engineer is depend- 
ent. It is also a work demanding, in most cases, unusual skill 
and care, and, to be satisfactory, must generally be performed 
either at the manufacturer's, or at the office of the engineer 
conducting the trial. The scales can usually be standardized 
by the official sealer of weights and measures, and sealed by 
him ; the water-meters, if used, can be readily tested by the use 
of the scales so sealed ; the thermometers are, as a rule, best 
tested by their makers, and should be sent to the maker for 
test immediately before and directly after the test. The 
engineer often has a carefully preserved standard with which 
they may be compared in his own office. The same remarks 
apply to the examination of the gauges used, which should be 
standardized both before and after their use. The apparatus 
used in connection with the calorimeter, in the determina- 
tion of the quality of the steam made, demand exceptional 
care in this process. Where it is unavoidable, the use of 
coarsely graduated thermometers and roughly constructed 
scales may be permitted, but only then when a very large 
number of observations are taken, and an average thus ob- 
tained which may befairly expected to fall within reasonable 
limits of error. 

The method of starting and of stopping the trial is a very 
important matter, and one upon which engineers of experience 
and acknowledged authority are not in complete accord. The 
principles to be adhered to in this matter, as in every other 
detail of the operation of testing a boiler, are easily specified, 
but they are not always as easy of practice. All conditions 
should be as exactly the same at the beginning and at the end 
of the test as they can possibly be made. The period of the 
trial and the times of stopping and of starting should be capa- 
ble of being exactly fixed, and the method of test should be 



492 THE STEAM-BOILER. 

such as should permit of the commencement and the end 
occurring at these exactly defined times, or, as an alterna- 
tive, they should be such that the work done by the boiler 
during the less precisely determinable time of beginning and 
ending of the trial should be as nearly as possible nil, so 
that a slight error as to time may not appreciably affect the 
results. 

During the trial, provision should be made for the preserva- 
tion of the utmost possible uniformity of working conditions 
throughout the whole period of the trial. Every irregularity 
gives rise to more or less loss of efficiency, and to uncertainty 
in regard to the correctness of the reported figures. The nearer 
the working of the boiler is kept to the final average for the 
trial, the better. 

Uniformity of operation and maximum efficiency are best 
attainable during a trial when a system of record is adopted 
which allows of that regularity being shown at all times ; and 
records in proper form are the best possible security against 
error of observation. Graphical methods should be adopted 
wherever practicable. Such methods of record exhibit most 
satisfactorily the accordance with or the deviation from the 
uniformity of operation considered so desirable on the score of 
efficiency and accuracy. 

255. Standard Test-trials are made under established sys- 
tems, and in accordance with codes of regulations which are 
accepted as representing a satisfactory system of procedure. 
In such cases the first step is to settle upon a standard of 
measurement and comparison that may be accepted by all who 
may be interested in the result. The standard nominal horse- 
power has already been described as now accepted by the best 
authorities. 

The Committee of Judges of the Centennial Exhibition, to 
whom the trials of competing boilers at that exhibition were 
intrusted, adopted the unit, ^o pounds of water evaporated into 
dry steam per hour from fee d-zvater at 100° Fahrenheit, and un- 
der a pressure of seventy pounds per square inch above tJie atmos- 
phere, these conditions being considered to represent fairly 



STEAM-BOILER TRIALS. 493 

average practice. The quantity of heat demanded to evaporate 
a pound of water under these conditions is 1110.2 British ther- 
mal units, or 1.1496 " units of evaporation." The unit of power 
prop'osed is thus equivalent to the development of 33,305 heat- 
units per hour, or 34.488 units of evaporation. The " unit of 
evaporation" is taken as a certain weight — preferably unity of 
water, evaporated " from and at " the boiling-point under atmos- 
pheric pressure. The now-accepted unit of boiler-power, in the 
code constructed for the American Society of Mechanical En- 
gineers," is the equivalent of the Centennial Standard, and in 
all standard trials the commercial horse-power is taken as an 
evaporation of 30 pounds of water per Jionr from a feed-water 
temperature of 100° Fahr. into steam at 70 pounds gauge-pres- 
sure, which is equal to 34^- units of evaporation, that is, to 34J 
pounds of water evaporated from a feed-water temperature of 
212° Fahr. into steam at the same temperature. This standard 
is equal to 33,305 thermal units per hour.f 

A boiler rated at any stated horse-power should be capable 
of developing that power with easy firing, moderate draught 
and ordinary fuel, while exhibiting good economy ; and the 
boiler should be capable of developing one half or one third 
more than its rated power to meet emergencies at times when 
maximum economy is not the most important object to be at- 
tained. 

256. Instructions and Rules governing the standard sys- 
tem of boiler-trial, prepared by a committee of the American 
Society of Mechanical Engineers, may be taken as a good illus- 
tration of such regulations as, in one form or another, have 
been customarily agreed upon by engineers conducting such 
work. They are as follows : 



* Transactions, vol. vi., 1884. 

f An evaporation of 30 pounds of water from 100° F. into steam at 70 pounds 
pressure is equal to an evaporation of 34.488 pounds from and at 212°; and an 
evaporation of 34^ pounds from and at 212° F. is equal to 30.010 pounds from 
100° F., into steam at 70 pounds pressure. 

The "unit of evaporation" being equal to 965.7 thermal units, the commercial 
horse-power is 34.488 X 965.7 = 33.305 thermal units. 



494 THE STEAM-BOILER. 

PRELIMINARIES TO A TEST. 

I. In preparing for and conducting trials of steam-boilers, 
the specific object of the proposed trial should be clearly defined 
and steadily kept in view. 

II. Measure and record the dimensions, position, etc., of grate 
and heating surfaces, flues and chimneys, proportion of air-space 
in the grate-surface, kind of draught, natural or forced. 

III. Put the Boiler in good condition. — Have heating-surface 
clean inside and out, grate-bars and sides of furnace free from 
clinkers, dust and ashes removed from back connections, leaks 
in masonry stopped, and all obstructions to draught removed. 
See that the damper will open to full extent, and that it may 
be closed when desired. Test for leaks in masonry by firing a 
little smoky fuel and immediately closing damper. The smoke 
will then escape through the leaks. 

IV. Have an understanding with the parties in whose inter- 
est the test is to be made as to the character of the coal to be 
used. The coal must be dry, or, if wet, a sample must be dried 
carefully and a determination of the amount of moisture in the 
coal made, and the calculation of the results of the test corrected' 
accordingly. 

Wherever possible, the test should be made with standard 
coal of a known quality. For that portion of the country 
east of the Alleghany Mountains good anthracite ^^^ coal 
or Cumberland semi-bituminous coal may be taken as the 
standard for making tests. West of the Alleghany Mountains 
and east of the Missouri River, Pittsburg lump coal may be 
used.* 

V. In all important tests a sample of coal should be selected 
for chemical analysis. 

VI. Establish the correctness of all apparatus used in the test 
for weighing and measuring. These are : 

* These coals are selected because they are almost the only coals which con- 
tain the essentials of excellence of quality, adaptability to various kinds of fur- 
naces, grates, boilers, and methods of firing, and wide distribution and general 
accessibility in the markets. 



STEAM-BOILER TRIALS. 495 

1. Scales for weighing coal, ashes, and water. 

2. Tanks, or water-meters for measuring water. Water- 
meters, as a rule, should only be used as a check on other meas- 
urements. For accurate work, the water should be weighed or 
measured in a tank. 

3. Thermometers and pyrometers for taking temperatures 
of air, steam, feed-water, waste gases, etc. 

4. Pressure-gauges, draught-gauges, etc. 

VI I. Before beginning a test, the boiler and chimney should 
be thoroughly heated to their usual working temperature. If 
the boiler is new, it should be in continuous use at least a week 
before testing, so as to dry the mortar thoroughly and heat the 
walls. 

VIII. Before beginning a test, the boiler and connections 
should be free from leaks, and all water-connections, including 
blow and extra-feed pipes, should be disconnected or stopped 
with blank flanges, except the particular pipe through which 
water is to be fed to the boiler during the trial. In locations 
where the reliability of the power is so important that an extra 
feed-pipe must be kept in position, and in general Avhen for any 
other reason water-pipes other than the feed-pipes cannot be 
disconnected, such pipes may be drilled so as to leave openings 
in their lower sides, which should be kept open throughout the 
test as a means of detecting leaks, or accidental or unauthorized 
opening of valves. During the test the blow-off pipe should 
remain exposed. 

If an injector is used, it must receive steam directly from the 
boiler being tested, and not from a steam-pipe, or from any 
other boiler. 

See that the steam-pipe is so arranged that water of con- 
densation cannot run back into the boiler. If the steam-pipe 
has such an inclination that the water of condensation from any 
portion of the steam-pipe system may run back into the boiler, 
it must be trapped so as to prevent this water getting into the 
boiler without being measured. 



49^ THE STEAM-BOILER. 

STARTING AND STOPPING A TEST. 

A test should last at least ten hours of continuous running 
and twenty-four hours whenever practicable. The conditions 
of the boiler and furnace in all respects should be, as nearly as 
possible, the same at the end as at the beginning of the test. 
The steam-pressure should be the same, the water-level the 
same, the fire upon the grates should be the same in quantity 
and condition, and the walls, flues, etc., should be of the same 
temperature. To secure as near an approximation to exact 
uniformity as possible in conditions of the fire and in tempera- 
tures of the walls and flues, the following method of starting 
and stopping a test should be adopted : 

X. Standard Method. — Steam being raised to the working 
pressure, remove rapidly all the fire from the grate, close the 
damper, clean the ash-pit, and as quickly as possible start a new 
fire with weighed wood and coal, noting the time of starting 
the test and the height of the water-level while the water is in 
a quiescent state, just before lighting the fire. 

At the end of the test, remove the whole fire, clean the 
grates and ash-pit, and note the water-level when the water is' 
in a quiescent state ; record the time of hauling the fire as the 
end of the test. The water-level should be as nearly as pos- 
sible the same as at the beginnihg of the test. If it is not the 
same, a correction should be made by computation, and not by 
operating pump after test is completed. It will generally be 
necessary to regulate the discharge of steam from the boiler 
tested by means of the stop-valve for a time while fires are 
being hauled at the beginning and at the end of the test, in 
order to keep the steam-pressure in the boiler at those times 
up to the average during the test. 

XI. Alternate Method. — Instead of the Standard Method 
above described, the following may be employed where local 
conditions render it necessary : 

At the regular time for slicing and cleaning fires have 
them burned rather low, as is usual before cleaning, and then 
thoroughly cleaned ; note the amount of coal left on the 
grate as nearly as it can be estimated ; note the pressure of 



STEAM-BOILER TRIALS. 49/ 

steam and the height of the water-level — which should be at 
the medium height to be carried throughout the test — at the 
same time ; and note this time as the time of starting the test. 
Fresh coal, which has been weighed, should now be fired. The 
ash-pits should be thoroughly cleaned at once after starting. 
Before the end of the test the fires should be burned low, just 
as before the start, and the fires cleaned in such a manner as to 
leave the same amount of fire, and in the same condition, on the 
grates as at the start. The water-level and steam-pressure 
should be brought to the same point as at the start, and the 
time of the ending of the test should be noted just before fresh 
coal is fired. 

DURING THE TEST. 

XII. Keep the Conditions Uniform. — The boiler should be 
run continuously, without stopping for meal-times or for rise 
or fall of pressure of steam due to change of demand for steam. 
The draught being adjusted to the rate of evaporation or com- 
bustion desired before the test is begun, it should be retained 
constant during the test by means of the damper. 

If the boiler is not connected to the same steam-pipe with 
other boilers, an extra outlet for steam with valve in same 
should be provided, so that in case the pressure should rise to 
that at which the safety-valve is set, it may be reduced to the 
desired point by opening the extra outlet, without checking 
the fires. 

If the boiler is connected to a main steam-pipe with 
other boilers, the safety-valve on the boiler being tested should 
be set a few pounds higher than those of the other boilers, so 
that in case of a rise in pressure the other boilers may blow oil^ 
and the pressure be reduced by closing their dampers, allowing- 
the damper of the boiler being tested to remain open, and firing 
as usual. 

All the conditions should be kept as nearly uniform as pos- 
sible, such as force of draught, pressure of steam, and height of 
water. The time of cleaning the fires will depend upon the 
character of the fuel, the rapidity of combustion, and the kind 
of grates. When very good coal is used, and the combustion 
not too rapid, a ten-hour test may be run without any cleaning 

2-2 



49 S THE STEAM-BOILER. 

of the grates, other than just before the beginning and just be- 
fore the end of the test. But in case the grates have to be 
cleaned during the test, the intervals between one cleaning and 
another should be uniform, 

XIII. Keeping the Records. — The coal should be weighed 
and delivered to the firemen in equal portions, each sufficient 
for about one hour's run, and a fresh portion should not be de- 
livered until the previous one has all been fired. The time 
required to consume each portion should be noted, the time be- 
ing recorded at the instant . of firing the first of each new por- 
tion. It is desirable that at the same time the amount of water 
fed into the boiler should be accurately noted and recorded, in- 
cluding the height of the water in the boiler, and the average 
pressure of steam and temperature of feed during the time. By 
thus recording the amount of water evaporated by successive 
portions of coal, the record of the test may be divided into sev- 
eral divisions, if desired, at the end of the test, to discover the 
degree of uniformity of combustion, evaporation, and economy 
at different stages of the test. 

XIV. Priming Tests. — In all tests in which accuracy of re- 
sults is important, calorimeter tests should be made of the per- 
centage of moisture in the steam, or of the degree of super- 
heating. At least ten such tests should be made during the 
trial of the boiler, or so many as to reduce the probable average 
error to less than one per cent, and the final records of the 
boiler test corrected according to the average results of the 
calorimeter tests. 

On account of the difficulty of securing accuracy in these 
tests the greatest care should be taken in the measurements of 
weights and temperatures. The thermometers should be ac- 
curate to within a tenth of a degree, and the scales on which 
the water is weighed to within one hundredth of a pound. 

ANALYSES OF GASES. — MEASUREMENT OF AIR-SUPPLY, ETC. 

XV. In tests for purposes of scientific research, in which the 
determination of all the variables entering into the test is de- 
sired, certain observations should be made which are in general 
not necessary in tests for commercial purposes. These are the 
measurement of the air-supply, the determination of its con- 



STEAM-BOILER TRIALS. 



499 



tained moisture, the measurement and analysis of the flue- 
gases, the determination of the amount of heat lost by radiation, 
of the amount of infiltration of air through the setting, the 
direct determination by calorimeter experiments of the absolute 
heating value of the fuel, and (by condensation of all the steam 
made by the boiler) of the total heat imparted to the water. 

The analysis of the flue-gases is an especially valuable 
method of determining the relative value of different methods 
of firing, or of different kinds of furnaces. In making these 
analyses great care should be taken to procure average samples, 
since the composition is apt to vary at different points of the 
flue, and the analyses should be intrusted only to a thoroughly 
competent chemist, who is provided with complete and accurate 
apparatus. 

As the determination of the other variables mentioned above 
are not likely to be undertaken except by engineers of high 
scientific attainments, and as apparatus for making them is 
hkely to be improved in the course of scientific research, it is 
not deemed advisable to include in this code any specific direc- 
tions for making them. 

RECORD OF THE TEST. 
XVI. A '' log" of the test should be kept on properly pre- 
pared blanks, containing headings as follows : 





Pressures. 


Temperatures.. i 


Fuel. 


Feed- 
water. 


Time. 


a; 

03 . 


t 

s 

e 

1 


f 

Q 


< 
1 

1 


o 


6 


% 


% 




c 


i 


d 

o 
•a 

G 
S 










1 



















500 



THE STEAM-BOILER, 



REPORTING THE TRIAL. 
XVII. The final results should be recorded upon a properly- 
prepared blank, and should include as many of the following 
items as are adapted for the specific object for which the trial 
is made. The items marked with a "^ may be omitted for or- 
dinary trials, but are desirable for comparison with similar data 
from other sources. 



Results of the trials of a. 

Boiler at , 

To determine 



1. Date of trial 

2. Duration of trial, 



DIMENSIONS AND PROPORTIONS. 

Leave space for complete description. See Ap- 
pendix XXIII. 

3. Grate- surface. . . =wide. . . .long. . . .Area. . . . 

4. Water-heating surface 

5. Superheating-surface 

6. Ratio of water heating surface to grate-sur- 

face 



7. 
*8. 

10. 



■22. 



AVERAGE PRESSURES. 

Steam-pressure in boiler, by gauge. . . 

Absolute steam-pressure 

Atmospheric pressure, per barometer. 
Force of draught in inches of water. . , 

AVERAGE TEMPERATURES. 

Of external air 

Of fire-room 

Of steam 

Of escaping gases 

Of feed- water 



FUEL. 

Total amount of coal consumed f 

Moisture in coal 

Dry coal consumed 

Total refuse, dry pounds = 

Total combustible (dry weight of coal, Item 

18, less refuse, Item 19) 

Dry coal consumed per hour 

Combustible consumed per hour 



hours. 



sq. ft. 
sq. ft. 
sq. ft. 



lbs. 
lbs. 
in. 
in. 



deg. 
deg. 
deg. 
deg. 
deg. 



lbs. 
per cent. 

lbs. 
per cent. 

lbs. 
lbs. 
lbs. 



* See reference in paragraph preceding table. 

f Including equivalent of wood used in lighting fire, i pound of wood 
equals 0.4 pound coal. Not including unburnt coal withdrawn from fire at end 
of test. 



STEAM-BOILER TRIALS. 



501 



23. 



24- 

25. 



26. 

27. 
28. 
^29. 
30. 



31- 



32. 
33- 



RESULTS OF CALORIMETRIC TESTS. 

Quality of steam, dry steam being taken as 

unity 

Percentage of moisture in steam 

Number of degrees superheated 



Total weight of water pumped into boiler 

and apparently evaporated *..... 

Water actually evaporated, corrected for 

quality of steam f 

Equivalent water evaporated into dry steam 

from and at 212° F.f 

Equivalent total heat derived from fuel in 

British thermal units f 

Equivalent water evaporated into dry steam 

from and at 212° F. per hour 



ECONOMIC EVAPORATION. 

Water actually evaporated per pound of dry 
coal, from actual pressure and tempera- 
ture f 

Equivalent water evaporated per pound of 
dry coal from and at 212° F.f 

Equivalent water evaporated per pound of 
combustible from and at 212° F.f 



per cent, 
deg. 



lbs. 
lbs. 
lbs. 

B. T. U. 

lbs. 

lbs. 
lbs. 
lbs. 



* Corrected for inequality of water-level and of steam-pressure at beginning 
and end of test. 

f The following shows how some of the items in the above table are de- 
rived from others: 

Item 27 = Item 26 X Item 23, 

Item 28 — Item 27 X Factor of evaporation. 

H - h ^^ 

, Hand h being respectively the total heat- 



Factor of evaporation = 



965-7 

units in steam of the average observed pressure and in water of the average 
observed temperature of feed, as obtained from tables of the properties of steam 
and water. 

Item 29 = Item 27 X {H — h). 

Item 31 = Item 27 -J- Item 18. 

Item 32 = Item 28 -^ Item 18 or = Item 31 X Factor of evaporation. 

Item 33 = Item 28 -r- Item 20 or = Item 32 -f- (per cent 100 — Item 19). 

Items 36 to 38. First term = Item 20 X - 

5 
Items 40 to 42. First term = Item 39 X o ' 

Item 43 = Item 29 X 0.00003 or = ^"^ ^^ 

34i 
,, Difference of Items 43 and 44 

Item 45 = ii -13. 

Item 44. 



502 



THE STEAM-BOILER. 



34. 



35- 



*36. 
*37. 
*38. 



39- 

*42. 

43. 

44. 

45. 



COMMERCIAL EVAPORATION. 

Equivalent water evaporated per pound of 
dry coal with one sixth refuse, at 70 pounds 
gauge-pressure, from temperature of 100° 
F. = Item 33 multiplied by 0.7249 



RATE OF COMBUSTION. 

Dry coal actually burned per square foot of 
grate-surface per hour 

] Per sq. ft. of grate- 
Consumption of I surface... 

dry coal per hour, i Per sq. ft. of water 

Coal assumed with f heating surface 

one sixth refuse. f Per sq. ft. of least 
J area for draught. . . 

RATE OF EVAPORATION. 

Water evaporated from and at 212° F. per 

square foot of heating-surface per hour. . . 

f Water evaporated ] Per sq. ft. of grate- 

per hour from tern- | surface 

perature of 100° F. ! Persq. ft. of water- 
heating surface 



into steam of 70 
pounds gauge-pres- 
sure, f 



Per sq. ft. of least 
area for draught. 



COMMERCIAL HORSE-POWER. 

On basis of thirty pounds of water per hour 
evaporated from temperature of 100° F. 
into steam of 70 pounds gauge pressure, 
( = 34i lbs. from and at 212°) f 

Horse-power, builders' rating, at square 

feet per horse power 

Per cent developed above, or below, rat- 
ing! 



lbs. 

lbs. 
lbs. 
lbs. 
lbs. 

lbs. 
lbs. 
lbs. 
lbs. 



H. P. 
H. P. 

Per cent. 



257* Precautions are to be taken in every possible way to 
prevent and avoid irregularities in the conduct of the trial and 
errors of observation.^ 

In preparing for and conducting trials of steam-boilers the 
specific object of the proposed trial should be clearly defined 
and steadily kept in view, and as suggested by Mr. Hoadley — 

(i) If it be to determine the efficiency of a given style of 
boiler or of boiler-setting under normal conditions, the boiler 
brickwork, grates, dampers, flues, pipes, in short, the whole ap- 
paratus, should be carefully examined and accurately described, 

* The appendix to the report above quoted should be read in this connection. 



STEAM-BOILER TRIALS. 503 

and any variation from a normal condition should be remedied, 
if possible, and if irremediable, clearly described and pointed out. 

(2) If it be to ascertain the condition of a given boiler or 
set of boilers with a view to the improvement of whatever may 
be faulty, the conditions actually existing should be accurately 
observed and clearly described. 

(3) If the object be to determine the relative value of two 
or more kinds of coal, or the actual value of any kind, exact 
equality of conditions should be maintained if possible, or, 
where that is not practicable, all variations should be duly al- 
lowed for. 

(4) Only one variable should be allowed to enter into the 
problem ; or, since the entire exclusion of disturbing variations 
cannot usually be effected, they should be kept as closely as 
possible within narrow limits, and allowed for with all possible 
accuracy. 

Blanks should be provided in advance, in which to enter all 
data observed during the test. The preceding instructions 
contain the form used in presenting the general results. Rec- 
ords should be, as far as possible, made in a standard form, in 
order that all may be comparable. 

The observations must be made by the engineer conduct- 
ing the trial, or by his assistants, with this object distinctly in 
mind ; and each should have a well-defined part of the work 
assigned him, and should assume responsibility for that part, 
having a distinct understanding in regard to the extent of 
his responsibility, and a good idea of the extent and nature 
of the work done by his colleagues, and the relations of each 
part to his own. No observations should be permitted to be 
made by unauthorized persons for entrance upon the log ; 
and no duties should be permitted to be delegated by one as- 
sistant to another, without consultation and distinct under- 
standing with the engineer in charge. The trial should, wher- 
ever possible, be so conducted that any error that may occur in 
the record may be detected, checked, or, if advisable, removed, 
by some process of mutual verification of related observations. 
It is in this direction that the use of graphical methods of rec- 
ord and automatic instruments have greatest value. 



504 THE STEAM-BOILER. 

Several methods of weighing fuel have been found very satis- 
factory, but it should be an essential feature that the weights 
shall be made by one observer and checked by another, at as 
distant a point as is convenient. The weighing of the fuel by 
one observer at the point of storage, and the record at that 
point of times of delivery, as well as of weights of each lot, and 
the tallying of the number and record of the time of receipt at 
the furnace-door, will be usually found a safe system. The fail- 
ure to record any one weight leads to similar error, and can 
only be certainly prevented by an effective method of double 
observation and check. 

The same remarks apply, to a considerable extent, to the 
weighing of the water fed to the boiler. A careful arrangement 
of weighing apparatus, a double set of observations, where pos- 
sible, and thus safe checks on the figures obtained, are essential 
to certainty of results. With good observers at the tank, and 
with small demand for water, a single tank can be used ; but 
two are preferable in all cases, and three should be used if the 
work demands very large amounts of feed-water, as at trials of 
very large boilers, or «^f " batteries." The more uniform the 
water-supply, as well as the more steady the firing, the less the 
liability to mistake in making the record. 

The two blanks which follow were prepared by the Author 
for use in laboratory as well as professional work. 

258. The Results of Trials actually conducted under ac- 
ceptable conditions, and with all the precautions which have 
been advised, are illustrated by the following examples : 

The first case was a trial which was carried out in ac- 
cordance with the above programme. The measurements of 
the feed-water were made by passing the water through a 
Worthington metre into two wooden tanks located on Fair- 
banks Standard Platform Scales. The pipe connections were 
so arranged that one tank could be filled and weighed 
while the other tank was being emptied into the boiler. 

Each tank was filled once every half hour. As soon as the 
tank was full and the pumping into the boiler commenced, the 
temperature of the feed-water was taken by sensitive ther- 
mometers reading to one-tenth of a degree. 



STEAM-BOILER TRIALS. 



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STEAM-BOILER TRIALS, 



507 



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50S THE STEAM-BOILER. 

The measurements of the coal were effected by weighing 
the coal previous to its being wheeled into a pile m the coal- 
room. The second weighing was made when the coal was fed 
into the furnace. As far as it was possible, the furnace was 
supplied with coal at intervals of every half hour, so as to 
correspond as nearly as could be to the feeding of the water. 

After the completion of the test, a careful analysis of the 
coal was made, to determine upon a sufficiently large scale its 
calorific power and the quantity of contained moisture. The 
steam from the boiler was condensed by means of a continu- 
ously acting calorimeter, formed by placing four tanks on 
Fairbanks Standard Platform Scales. The steam from the 
boiler was passed through a surface-condenser having a 
condensing surface of 631 sq. ft. As fast as the steam was con- 
densed from the boiler it was received in small tanks located 
on platform-scales. These tanks were similar in size to the 
feed-water tanks, and were so arranged as to be filled and 
emptied once every half hour, one tank receiving the condensed 
water from the boiler while the other was being emptied. 

The condenser was supplied with a large volume of cold 
water from a weir just outside of the works, and after flowing 
through the condenser and thereby cooling the steam and 
receiving therefrom the contained heat, this water was caught 
in two large tanks placed on platform-scales. These tanks were 
also arranged so that one tank could be emptied while the 
other was being filled, and were of sufficient capacity so as to 
insure catching all of the water required for half an hour's run 
in the condenser. The temperature of the inlet water of the 
condenser, of the outlet water, and of the condensed steam 
were carefully noted by means of thermometers reading to a 
tenth of a degree. Readings of the inlet water and of the 
condensed steam were taken once every half hour at the 
same time that the quantities of the water in the tanks were 
weighed. Inasmuch as the outlet to the condenser varied 
considerably in temperature, readings on this were taken every 
five minutes during the entire time of the test. It will thus be 
seen that a very correct average of the amount of heat given to 
the condenser was obtained. The quantity of air supplied 



STEAM-BOILER TRIALS. SOQ 

by the blowers to the furnace was measured by continuously 
acting anemometers placed in the supply-pipes. The readings 
of the anemometers were checked by means of the number of 
revolutions of the blowers and their cubic feet per revolution. 

The steam-pressure was kept by a recording pressure-gauge, 
which was checked by an exceedingly delicate and sensi- 
tive gauge, which previously, and subsequently to the test, 
was carefully verified by means of a mercury column. Constant 
records of the hygrometer, barometer, and thermometers, both 
in the boiler-room and of the external air, were kept during the 
entire period of the test. 

It will be seen from the above, that all of the processes and 
measurements were kept in duplicate in such a way as to afford 
a constant check on each other and preclude the possibility of 
any errors. 

Samples of steam were taken in a small calorimeter for the 
purpose of ascertaining whether the boiler supplied wet steam. 

The following is a brief condensed summary : 

Efficiency as Per Test, 7.50 a.m. to 7.50 a.m. 

Total heat of boiler 64,536,613 heat-units. 

Steam 42,933,141 " " 66.6 per cent. 

Heat escaping in flue -gases 9,669,036 " " 15 " " 

Radiated heat 5,162,939 " " 8 " " 

Heat to vaporize moisture in 

coal 141,372 " " 0.2 " '* 

Heat to vaporize moisture in 

air supplied to furnace 345,978' " " 0.4 " " 

Leakage 3.531,645 " " 4.0 " " 

" from pump 127,936 " " 0.2 " " 

Heat absorbed by fire-brick 2,581,645 " " 4.0 ** " 

Unaccounted for 1,092,941 " " 1.6 " " 

In the trial of an upright boiler reported on by Sir Frederick 

Bramwell, in 1876, coke being used as the fuel and wood in 

starting the fires, the following data* were obtained : 

Ash and moisture 43-79 lbs. 

Combustible^ 194.46 " 

Totalfuel 238.25 " 

Air used per pound combustible. I7i " 

* Conversion of Heat into Work. Anderson. 



510 



THE STEAM-BOILEK. 



Heat generated, net 2 

" " per lb. fuel 

" " available, net 2 

Water evaporated 

The efficiency of the furnace was 

The balance-sheet stands thus : 

Dr, 

Available heat 2, 

Cr. 
Per Cent. 

88.29 Heat expended in evaporation i, 

7.03 Displacing atmosphere 

3.35 Loss by conduction and radiation 

.05 Heat in ashes 

1 . 26 Unaccounted for 



798,312 

11,745 

101,700 

1,620 

0.643 



B. T. U. 



lbs. 



101.700 B. T. U» 



855,900 

147,720 

70,430 

1,129 

25.521 



100.00 2,101,700 

The following are data from a trial of a Galloway boiler, 
as reported to the Edgemoor Iron Co., in the year 1885, 
by Messrs. G. N. Comly and R. Dawes, and the efficiency 
too near the theoretical maximum to be often duplicated. 
The boiler tested was fitted with an " economizer," or feed- 
water heater, and the power developed was considerably under 
its rating. The fuel was a Pennsylvania bituminous. The 
draught was obtained by a high chimney, and was, as shown in 
the table, quite powerful. The tabular statement is mainly 
given as illustrating a very compact form of record of results. 

TABLE OF RESULTS OF THE TEST OF A GALLOWAY BOILER AT 
FRANKFORD JUNCTION, PHILADELPHIA, PA. 



Dimensions 

AND 

Proportions: 



Average 
Pressures: 



Date of Trial 

Duration of Trial 

Height of Stack . . . . . 

Boiler, seven feet in diameter, twenty-eight 
feet long. 

Grate-surface 

Water-heating-surface 

Superheating-surface 

Ratio of Water-heating Surface to Grate-sur- 
face 

Economizer Heating-surface, per each boiler 

' Force of Draught, in inches, at stack base 

after leaving economizer ... 

Force of Draught, in inches, at back of boiler 

before entering economizer 
Force of Draught, in inches, at front of boiler 

before entering economizer 
Absolute Steam-pressure .... 
Atmospheric Pressure, per barometer 
[ Steam-pressure in boiler, by gauge 



April 8th, 1885. 
ii34 hours. 
200 feet. 



35.75 sq. ft. 

853 

225 " 

23.86 to I sq. ft. 
609 sq. ft. 



.75 ins. of water. 
.5625 

.6063 
93-575 pounds, 
29.975 inches. 
78.875 pounds. 



STEAM-BOILER TRIALS. 



511 



Average 
Temperatures: 



Fuel: 



Results of 

Calorimetric 

Tests: 



Water: 



Economic 
Evaporation; 



Rate of 
Combustion: 



Of External Air 

Of Fire-room 

Of Steam 

Of Chimney-flue, escaping gases 

Of Side-flue, at back end of boiler, escaping 

gases 

Of Side-flue, at front end of boiler, escaping 

gases ........ 

Of Feed-water 

Of Feed-water, after leaving econcmizer, and 

entering boiler 

' Total amount of Coal consumed 

Total Refuse from coal 

Moisture in Coal 

Total Combustible 

Dry Coal consumed, per hour .... 

Combustible consumed, per hour 

Dry Coal consumed, per indicated horse-power, 
per hour 

Combustible consumed, per indicated horse- 
power, per hour 



r Quality of Steam, dry steam being taken as 

J unity 

I Percentage of Moisture in steam 
[ Number of Degrees superheated 

' Height of Water in gauge-glasses 
Total weight of Water pumped into boiler 

Of this there was used as hot water . 
Converted into Steam 
Water actually evaporated, corrected for qual- 
ity of steam 

Equivalent Water evaporated into dry steam 

from and at 212° F 

Percentage of increase of Evaporative Capacity 

by using economizer ..... 
Equivalent Water evaporated into dry steam 

from and at 212° F. per hour 
Equivalent total Heat derived from fuel, in 

British thermal units 

Equivalent total Heat derived from one pound 

of dry coal ....... 

Equivalent total Heat derived from one pound 

of combustible . . . . . 



Water actually evaporated, per pound of drj' 
coal, from actual pressure and temperature 

Water actually evaporated, per pound of com- 
bustible 

Equivalent Water evaporated, per 
pound of dry coal, from and at 
212° F 

Equivalent Water evaporated, per 
pound of combustible, from 
and at 212° F. . . . 

Equivalent Water evaporated, per I 
pound of combustible, from^ 
and at 212° F. 



Boiler and 

Economizer 

used 

together. 



By boiler 
exclusive 
of econo- 
mizer. 



■( 



' Dry Coal actually burned, per square foot of 
grate-surface, per hour .... 
Consumption of dry- f Per square foot of grate- 
Coal per hour, coal J surface 
assumed with onel Per square foot of 
sixth refuse, (_ water-heating surface . 



58 degrees. 

66 
381 " 
200 '* 

360 " 

589 " 
84 " 

155 " 

6925 pounds. 

569 

301 " 
6055 *' 

589 

538 " 

1.87 '' 
1.72 " 



1. 019984. 

None. 

58 degrees. 



4.63 inches. 
68, 138 pounds. 

2,782 " 
65,356 " 

66,854 " 

78,112 " 

6^ per cent. 
J 6943 pounds. 
( 116 cubic feet. 

75.432885. 

.11389. 

.12459. 



10.093 pounds. 
11.041 " 



"•79J 
12.907 

12.153 

16.46 
18.07 
0-745 



$12 THE STEAM-BOILER 



Water evaporated from and at 212° F., per 
square foot of water-heating surface, per 
hour 

Water evaporated, per hour, f Per square foot 
from temperature of | of grate-surface 
100° F. into steam of-j Per square foot 
seventy pounds' gauge- of water-heat- 
pressure, [ ing surface 



Rate of 
Evaporation: 



Horse-power of engine, as per indicator-cards 
taken on day of boiler-test . . 

Kind of Coal used 

Condition of Chimney-damper .... 

Cleaned fires, number of times on each fur- 
nace during the test 



8. 139 pounds. 
168.9 " 

7.079 



311.45 horse-power. 
Ocean bituminous. 
58 p.c. of fuUopen'g. 



In trials conducted by the Author, for a committee of the 
American Institute, of which he was chairman, in testing a 
number of different types of boiler,^ a surface-condenser was 
employed to condense all steam made, and results thus for the 
first time obtained which gave exact measures of net efficiency, 
the quality of all steam made being determined. 

In calculating the results from the record of the logs, the 
committee first determined the amount of heat carried away by 
the condensing water by deducting the temperature at which it 
entered from that at which it passed off. To this quantity is 
added the heat which was carried away by evaporation from 
the surface of the tank, as determined by placing a cup of 
water in the tank at the top of the condenser at such height 
that the level of the water inside and outside the cup were the 
same, noting the difference of temperatures of the water in the 
cup and at the overflow, and the loss by evaporation from the 
cup. The amount of evaporation from the surface of the 
water in the cup and in the condenser, which latter was ex- 
posed to the air, was considered as approximately proportional 
to the tension of vapor due their temperatures, and was so 
taken in the estimate. The excess of heat in the water of con- 
densation over that in the feed-water also evidently came from 
the fuel, and this quantity was also added to those already 
mentioned. 

* See Transactions. 1871; also, Report on Mechanical Engineering at Vienna 
International Exhibition, 1873, R. H. T. 



STEAM-BOILER TRIALS. 513 

The total quantities were, in thermal units, as follows : 

A 34,072.058.09 

B 48,241.833.60 

C 24,004,601.14 

D 38,737,217.57 

E , 11,951,002.10 

These quantities, being divided by the weight of combus- 
tible used in each boiler during the test, will give a measure of 
their relative economical efficiency ; and, divided by the num- 
ber of square feet of heating-surface, will indicate their relative 
capacity for making steam. But as it was the intention of the 
committee to endeavor to establish a practically correct meas- 
ure that should serve as a standard of comparison in subsequent 
trials, it was advisable to correct these amounts by ascertaining 
how and where errors have entered, and introducing the proper 
correction. There were two sources of error that are considered 
to have affected the result as above obtained. The tank beinsf 
of wood, a considerable quantity of water entered it, leaked out 
again at the bottom, without increase of temperature, instead 
of passing through the tank and carrying away the heat, as it 
is assumed to have done in the above calculation. The meters 
also registered rather more water than actually passed through 
them, and this excess assists in making the above figures too 
high. The sum of these errors the committee estimated at 
4 per cent of the total quantity of heat carried away by the 
condensing water. The other two quantities were considered 
very nearly correct. 

Making these deductions, we have the following as the total 
heat, in British thermal units, which was thrown into the con- 
denser by each boiler : 

A 32,75 1, 835 . 34 

B 46,387,827.10 

C 23,066,685.39 

D 37,228.739.07 

E 11,485,777-35 

That the figures thus obtained are very accurate, is shown 
by calculating the heat transferred to the condenser by the 
Root and the Allen boilers (both of which superheated their 
33 



514 THE STEAM-BOILER. 

steam), by basing the calculation on the temperature of the 
steam in the boiler, as given by the thermometer, the results 
thus obtained being 32,723,681.76 and 46,483,322.5, respec- 
tively. 

Dividing these totals by the pounds of combustible con- 
sumed by each boiler, we get as the quantity of heat per pound, 
and as a measure of the relative economic efficiency : 

A 10,281.53 

B 10. 246 . 92 

C 10,143.66 

D 10,048.24 

E 10,964.94 

Determining the weight, in pounds, of water evaporated per 
square foot of heating-surface per hour, we get as a measure of 
the steaming capacity : 

A 2.65 

B 3 59 

C 2.83 

D . . 3.10 

E 1.92 



The quantity of heat per pound of combustible, as above 
determined, being divided by the latent heat of steam at 212° 
Fahrenheit (966°. 6), gives as the equivalent evaporation of 
water at the pressure of the atmosphere, and with the feed at a 
temperature of 212° Fahrenheit: 

A — 10.64 

B 10.60 

C 10.49 

D 10.40 

E 10.34 

For general purposes this is the most useful method of com- 
parison for economy. 

The above figures afford a means of comparison of the 
boilers, irrespective of the condition (wet or dry) of the steam 
furnished by them. All other things being equal, however, 
the committee consider that boiler to excel which furnishes the 
driest steam ; provided that the superheating, if any, does not 
exceed about 100°. 



STEAM-BOILER TRIALS. 515 

In this trial the superheating was as follows : 

A 16'. 08 

B 13° 23 

• C o. 

D o. 

E o. 

As the boilers C, D, E did not superheat, it became an inter- 
esting and important problem to determine the quantity of 
water carried over by each with the steam. This we are able, 
by the method adopted, to determine with great facility and 
accuracy. 

Each pound of saturated steam transferred to the condens- 
ing water the quantity of heat which had been required to 
raise it from the temperature of the water of condensation to 
that due to the pressure at which it left the boiler, plus the heat 
required to evaporate it at that temperature. Each pound of 
water gives up only the quantity of heat required to raise it 
from the temperature of the water of condensation to that of 
the steam with which it is mingled. The total arnount of heat 
is made up of two quantities, therefore, and a very simple 
algebraic equation may be constructed which shall express the 
conditions of the problem : 

Let 

H = heat-units transferred per pound of steam. 

k = heat-units transferred per pound of water. 

U = total quantity of heat transferred to condenser. 
W = total weight of steam and water, or of feed-water. 

X = total weight of steam. 
W—x = total weight of water primed. 

Then 

Hx -\-/t{W-x)- U;orx = j. . 

Substituting the proper values in this equation, we deter- 



5i6 



THE STEAM-BOILER. 



mine the absolute weights and percentages of steam and water 
deHvered by the several boilers as follows : 





Weight of Steam. 


Weight of Water. 


Percentage of Water 

Primed to Water 

Evaporated. 


A 


27,896. 
39,670. 
19.782.94 
31,663.35 
9,855.6 


0. 

0. 

645 . 06 

2.336.65 

296.9 


0. 


B 


0. 


c 


3.26 


D 


6.9 
3. 


E 





And the amount of water, in pounds, actually evaporated 
per pound of combustible : 



8.76 
8.76 
8.70 
8.55 
9.41 



Comparing the above results, the committee were enabled 
to state the following order of capacity and of economy in the 
boilers exhibited, and their relative percentage of useful effect, 
as compared with the economical value of a steam-boiler that 
should utilize all of the heat contained in the fuel : 





Steaming Capacity. 


Economy of Fuel. 


Percentage 

of 

Economical Effect. 


A 


No. 4 
No. I 

No. 3 
No. 2 
No. 5 


No. 2 
No. 3 
No. 4 

No. 5 

No. I 


0.709 
0.707 
0.699 
0.693 
0.756 


B , 


c 


D 


E 





The results obtained as above, and other very useful deter- 
minations derived from this extremely interesting trial, were 
given in the table, as a valuable standard set of data with which 
to compare the results of future trials, and as a useful aid in 
judging of the accuracy of statements made by boiler-venders 
in the endeavor to effect sales by presenting extravagant claims 
of economy in fuel. 

Mr. Drewitt Halpin found the following net results of test of 
a variety of English-built boilers : 



STEAM-BOILER TRIALS. 



517 



No. 



Description of 
Boiler. 



Field 

Field 

Field 

Portable \ sjj . 
Portdble ( -.5 . 
Portable f i: . 
Portable ) (j . 

Lancashire 

Lancashire 

Lancashire 

Jacketed 

Lancashire. . .. 
Compound. .. . 
Loco. (Webb). 
Loco. (Marie). 
Loco. \ 

Loco: Coke.. 

Loco. ) 

Torpedo 

Torpedo 

Torpedo 

Torpedo 



Pounds W.a.ter 
Evaporated. 



u 'PC 



2.57 
1.52 
2.26 
1.76 
356 

1-57 
2.83 
1.88 
4.70 
2-57 
1-43 
9.83 
4.62 
12.57 
13-73 
6.76 

7-39 
12.54 
14.86 
17.90 
20.74 



o a C 
ag be 



8.83 
10.83 

10 93 
10.23 
10.49 
11.81 

9-93 
12.83 

9.89 
12.25 

7-7 
10.9 
11.51 
10.28 
10.65 
8.22 
8.94 
10.01 
11.2 

8-37 
7.78 

7-49 
7.04 
b 



THERM.A.L Units. 



14.718 
14,718 
14,718 



15.715 
13,833 
15,715 
14.805 
15-715 
14.296 
14.004 
14. 600 
13-550 
13,550 
13,550 
13,550 
14.727 
14,727 
14,727 
14,727 



o. .^ 
cr V- 

"^ V- ■" u 
^ «< tX3 

ill \. 



4,414 
2,202 
2,482 
1,468 
2,183 
1,700 
3,438 
1.516 
2,733 
1,816 
4»5Q5 



8,529 
10.461 
10.558 

9.882 
10,133 
11.408 

9-592 
12,393 

9-553 
"-833 

7- 500 
10.529 



1,381 


II. 125 


9,495 


9,930 


4,462 


10,287 


12,142 


7.940 


13,263 


8,636 


6.53c 


9,669 


7,138 


10,819 


12,113 


8,085 


14.354 


7.523 


17,291 


7.235 


20,034 


6.800 


d 


e 



II 

II w 

*j 4) 

ii U (U 



98.356 

148,444 

130 900 

118.248 
108.248 
185,844 

136.200 
229.750 
166.294 

107.718 

664.650 

312.340 
704,236 

835-569 

463,630 
549.626 
654,102 

732-054 
847.259 
921,564 
i 



The " locomotive" boiler is found to be more efficient as a 
part of the engine and on the track than when mounted as a 
stationary boiler, an unexpected result. 

259. The Quality of Steam made in any boiler, or as sup- 
plied to an engine, is hardly less important than the quantity. 
When the steam is required for heating purposes simply, or 
even when all the heat issuing as waste, necessary^ or other, 
from the exhaust-ports of a non-condensing engine cylinder 
can be utilized for useful and paying purposes, this is a matter 
of no importance; but when it is essential that loss in the 
engine shall be made a minimum, and that the engine shall 
have maximum efficiency, the quality of the steam becomes 
exceedingly important. Dry steam is very much more efficient 
as a working substance in the steam-engine than wet ; since, 
Avhere the latter is supplied from the boiler, the waste by 
cylinder-condensation is greatly increased — and so greatly that 
the more obvious direct loss by the passing of heat through 
the engine in unavailable form, hot water acting as its vehicle, 
becomes comparatively small. The determination of the quality 



5i8 



THE STEAM-BOILER. 



of steam by any boiler is thus as important as the measure of 
its apparent evaporation. 

The difference between the apparent and the actual evapo- 
ration is often very great. A good boiler properly managed 
will usually '' prime" less than five per cent, even though 
having no superheating-surface, and less than two per cent 
may usually be hoped for. Steam is often made practically 
dry. But a hard-w^orked boiler, or one having defective circu- 
lation, will often prime ten or twenty per cent ; and cases have 
been found in the experience of the Author in which the quan 
tity of water carried out of the boiler by the current of steam ex« 
ceeded the weight of the steam itself. It has thus happened 
that, where no measure of this defect has been made, the 
apparent evaporation only being reported, the quantity of water 
said to have been evaporated has equalled, and sometimes has 
even greatly exceeded, the theoretically possible evaporation of 
an absolutely perfect boiler. It is thus essential that, when the 
apparent evaporation has been determined by trial, the quantity 
of water entrained with the steam be measured and deducted, and 
then real evaporation thus ascertained and reduced for the 
standard conditions. Under ordinarily good conditions, a real 
evaporation of ten or eleven times the weight of the fuel, cor- 
responding to an efficiency of 0.75 to 0.80, represents the best 
practice, and a real evaporation of twelve of water by one of 
combustible, from and at the boiling-point, or an efficiency of 
eighty per cent, is rarely observed under the usually best con- 
ditions of steam-boiler practice. Where more than the efficiency 
here given as probable is reported, the work should be very care- 
fully revised, and errors sought until absolute certainty is 
secured. 

Trials not including calorimetric measurement of the water 
entrained with the steam are comparatively valueless, and 
should be rejected in any important case. Reports of extra- 
ordinary economy are often based on this kind of error. The 
experiments of M. Hirn at Mulhouse showed an average of about 
5 per cent priming ; Zeuner makes it approximately from j\ to 
15 per cent; while the experiments of the Author at the 
American Institute in 1871 give from 3 to 6.9 per cent. 



STEAM-BOILER TRIALS. 519 

A recently devised method of measuring the amount of 
moisture in the steam is to introduce into the boiler with the 
feed-.water sulphate of soda, and at intervals to draw from the 
lower gauge-cock a small amount of water, and also from the 
steam, condensing either by a coil of pipe in water or a small 
pipe in air. A chemical analysis gives the proportion of sul- 
phate of soda in each portion, and the quotient of the propor- 
tion of sulphate of soda in the portion from the steam by the 
proportion in that from the water gives the ratio of water 
entrained, as steam does not carry sulphate of soda, which is 
only brought over by the hot water entrained. This method 
was used by Professor Stahlschmidt at the Diisseldorf Exhibi- 
tion Trials. 

260. The Calorimeters used in determining the quantity 
of moisture in steam have several forms, widely differing in 
construction, and to some extent in value. They nearly 
all embody the same principles, however. The objects sought 
to be attained in their construction are : The exact measure- 
ment of the weight of steam received by them from the boiler, 
and of its temperature and pressure at the boiler ; the determi- 
nation of the weight of water used in its condensation and 
the range of temperature through which it is raised in the 
operation ; the reduction of wastes of heat in the calorimeter 
to a minimum, and the exact measurement of that waste if 
it is sensibly or practically noticeable. 

TJie Barrel or Tank Calorimeter as employed by the 
Author, is the simplest form of this instrument which has been 
employed. It consists of a strong barrel or tank, of hardwood, 
absorbing little of either water or heat, and having a movable 
cover. This tank is mounted on platform-scales capable of 
accurate adjustment and having as fine readings as possible. It 
is filled with water to within about one fourth its height from 
the top, and the steam is led into it through a rubber tube or 
hose of sufificient capacity to supply the steam to the amount 
of one eighth or one tenth the weight of the water in three 
or five minutes. A steam-gauge of known accuracy gives the 
boiler-pressure, and the corresponding temperature and total 
heat of the steam are ascertained from the steam-tables. 



520 



THE STEAM-BOILER. 



In using this apparatus the steam is rapidly passed into the 
mass of water contained in the tank, until the scales show 
that the desired quantity has been added. The steam is so 
directed by varying the position of the end of the tube, and 
by inserting it so deeply in the water that the whole mass is 
very thoroughly stirred, and a very perfect mixture secured of 
condensing water with the water of condensation ; and so that 
the temperatures indicated by the inserted thermometer shaU 
be the real mean temperature of the mass. The weights and 




Fig. 1 1 8. — The Calorimeter, 

temperatures are then inserted in the log of the trial, as below, 
and the proporticin of water brought over with the steam is 
thence easily calculable. The thermometers employed usually 
read to tenths of a degree- Fahrenheit, or to twentieths of a 
centigrade degree, accordingly as the one or the other scale is 
employed. Readings must be made with the greatest pos- 
sible accuracy, and in sufificient number to insure a satis- 
factorily exact mean. With good thermometers and scales, 
a reliable gauge, and care in operation, good results can be 
obtained by averaging a series of trials.^ 

The Hirn Calorimeter is substantially the same as the 
above, with the addition of an apparatus for stirring the water 



* Report on Boiler Trial, Trans. A. S. M. E. 1884, vol. vi. 



STEAM-BOILER TRIALS. $21 

in the tank to insure thorough mixture and readings of tem- 
perature of condensing water exactly representative of the true 
mean temperature of the mass after the introduction of the 
steam. This is not an essential feature of the apparatus, if the 
Author may judge by his own experience, provided the jet of 
entering steam is so directed as to cause rapid circulation. 
No stirring apparatus could operate more efficiently than 
the force of the steam itself, properly directed. Hirn was 
probably the first (1868) to attempt the determination of the 
quantity of steam as delivered from steam-boilers."^ A similar 
apparatus was used at the trials of the Centennial International 
Exhibition, Philadelphia, i876.t 

261. The Theory of the Calorimeter is as follows::]: 
Each pound of saturated steam transferred to the condens- 
ing water the quantity of heat w^hich had been required to 
raise it from the temperature of the water of condensation to 
that due to the pressure at which it left the boiler, plus the heat 
required to evaporate it at that temperature. Each pound of 
water gives up only the quantity of heat required to raise it 
from the temperature of the water of condensation to that of 
the steam, with which it is mingled. The total amount of 
heat is made up of two quantities, therefore, and a very simple 
algebraic equation may be constructed, which shall express the 
conditions of the problem : 

Let, as in § 258, 

H = heat-units transferred per pound of steam ; 

h = heat-units transferred per pound of water ; 

U = total quantity of heat transferred to condenser ; 
VV = total weight of steam and water, or of feed-water ; 

;ir = total weight of steam ; 
IV — X = total weight of water primed. 

* Bulletin de la Societe Industrielle de Mulhouse, 1868-9. 

f Reports of Judges, vol. vi. 

I First published by the Author, who had not then become aware of the work 
done by M. Hirn, in Trans. Am. Inst. Report on Boiler Trial, 18 71. See 
also Vienna Reports, vol. iii. p. 123. 



522 THE STEAM-BOILER. 

Then 

U 

Hx +^ (W-x)^ U', oxxz=.—^ = H-h ' 

Substituting the proper values in this equation, we deter. 
mine the absolute weights and percentages of steam and water 
delivered by the boiler. 

Or, let 

Q = quality of the steam, dry saturated steam being unity ; 
H^ = total heat of steam at observed pressure ; 
r = " " " water 

k' z= " " " condensing water, original ; 
/i^ — " " " " '' final. 

And we have the equivalent expression, as written by Mn 
Kent, 

I 



Q = 



H' -T 



[0-".)-(^-".)]- 



The value of the quantity U is obtained by multiplying the 
weight of water in the calorimeter originally by the range of 
temperature caused by the introduction of the steam from the 
boiler. Mr. Emery employs another form, as below, in which 
Q is the quality of steam as before ; W the weight of con- 
densing water ; w the weight added from the boiler ; T the 
temperature due the steam-pressure in the boiler ; t the initial 
and t^ the final temperature of the calorimeter ; / the latent 
heat of evaporation of the boiler-steam ; and x the weight of 
steam corresponding to /. Thus, 



w{t,^t)-w{T-t:) 

X , 



and 

X W{t, - t)-w{T- t^ 

w ~ 



Q- n.,- l^ 



S TEA M-B OIL ER TRIA IS. 



523 



If Q exceeds unity, the steam is superheated by the amount 



048 



= 2.0833/(2-/);* 



and if less than unity, the priming is, in per cent, 100 (i — Q). 
262. Records of calorimetric tests should be even more 
carefully and more frequently made than in any other part of 
the work of a boiler-trial. The following, from work conducted 
by the Author, illustrates the method. The symbols relate to 
the first of the above formulas. 

PRIMING TESTS. 









Calorimeter. 


Heat-units 




















PER Pound 


en ^" 


s 

la 


a 

f 


In 

« Q 

















r. 


Weights. 


Tempera- 
ture. 


FROM Boiler. 


c i; 






1^ 


i 








Water. 


Steam. 






^ 


c 








.• 1 


t 


T 


WxR 


H 


h =t 










e 


^ 


t/J S 


rt 




^rX. 






^U 


= T-t> 


— t' 


X 


y 


n 


a 


S 


c 




w 


.5^ 


^11 
















2 


H 


C/5 


U 


^ 




fe 


C^i< 


















a.m. 




























I 


Q.46 


21.5 


217.6 


H-7 


58. q 


123.2 


64-3 


262.851 


1193-59 


13991.68 


1070.39 


164.96 


12.827 


6.32 


2 


10.16 


3«. 


218. 1 


15.25 47.8 


121. 4 


73-6 


286.36 


1200.61 


16052.16 


1079.21 


14.806 


7.29 


3 


II. IS 
p.m. 
12. 01 


40. 


250. 


16.6546.7 


122.4 


75-7 


288.79 


1201.23 


18925. 


1078.83 


166.39 


17-705 


7-58 


4 


72.5 


250. 


18.3 


45.7 


124.2 


78.5 


320.88 


1210.87 


19625- 


1086.67 


196.68 


18.006 


7-77 


5 


1. 01 


bi.5 


250. 


18.2 


44.2 


121. 6 


77-4 


311.27 


1808.02 


19350. 


1086.42 


189.67 


17.728 


7.65 


6 


1.4s 


.S.S- 


2,SO. 


18.4s 


44.6 


123-7 


70.1 


305-07 


1209.19 


19775- 


1082.49 


181.37 


18.231 


7.82 


7 


2.25 


60. 


250. 


18.2 


44.2 


122.3 


78.1 


309.88 


1207.61 


19525- 


1085.31 


187.58 


17.946 


7-74 


8 


3.10 


61. 5 


250. 


16.92 44.6 


121. 7 


77.1 


311.27 


1208.02 


19275. 


1086.32 


189.57 


17.917 


7. 68 


9 


.3-55 


65- 


250. 


17. 1 


47-3 


121. 4 


74-1 


314-44 


1208.96 


18525. 


1087.56 


193.04 


17.019 


7 -,30 


10 


4-3° 


61. 


250. 


.7.. 


46.6 


120.0 


74.0 


310.81 


1207.88 


18500. 


1087.28 


190.21 


16.996 


7.29 



The boiler was a water-tubular boiler, which was not so 
handled as to give as dry steam as was desired ; and one object 
of the trial, of which the above is a part of the record, was to 
ascertain how seriously was the quality of the steam affected. 
It is seen that the priming amounted to seven or eight per 
cent, with fairly uniform figures through the period of test. The 
steam should have entrained less than one half this proportion, 
had the boiler been all that was expected of it. 

Errors of small magnitude, absolutely, may greatly affect 
the results of calculation, as is well illustrated by the following 
example presented by Mr. Kent : 



* Centennial Report, pp. 138-9. 



524 THE STEAM-BOILER, 

Assume the values of the quantities to be, as read, column i : 



Weight of condensing-water, corrected for 

equivalent of apparatus,* W 

Weight of condensed steam, w 

Pressure of steam by gauge, P 

Original temperature of condensing water, t.. 
Final temperature of condensing water, t' . . . . 



Observed 


True 


Reading. 


Reading. 


200.5 lbs. 


200 lbs. 


9.9 " 


lO.O " 


78. " 


80 " 


44°- 5 " 


45° " 


100°. 5 " 


100° " 



Amount of 
Error. 



^ pound, 

1 «< 
To 
2 pounds. 

-^ degree. 



Moisture 


Error 


per cent. 


per cent. 


Q = 0.9874 =1.26 


= 0. 


Q = .9906 = 0.94 


= 0.32 


Q = 1. 0000 = 0.00 


= 1.26 


Q = .9880= 1.20 


= 0.06 


Q= .9989 = 0.11 


= 1.15 


Q = .9994 = 0.06 


= 1.20 



Then let it be assumed that errors of instruments or of ob- 
servation have led to the recording of slightly different figures 
from the true quantities, as given in column 2 : 

Substituting in the formula the ' ' true 

readings," we have for the value of 

All readings true except JV = 200.5, 

" " " " 7£/ = 9.9, 

'' F = 78.0, 

" z" = 44.5, 
" " " " t' = 100.5, 
" " incorrect Q = 1.0272 = (minus)= 3.98 

The last case is equivalent to 50.2 degrees superheating. 

Errors of o.i or even 0.25 per cent in weights and of tem- 
perature of equal amount not infrequently occur, probably, 
where ordinary instruments are employed. The errors due 
to false weight in measurement of the condensed steam are 
liable to be very serious, and it is only by making a consider- 
able number of observations and obtaining the mean that re- 
sults can be secured, ordinarily, of real value. 

263. The " Coil Calorimeter" has been devised to secure 
more exact results in the weighing of the water of condensation 
than can be obtained when it is weighed as part of the larger 
mass. In this instrument a coil of pipe is introduced into the 
tank and serves as a surface-condenser in which the boiler-steam 
is received and condensed, and from which it is transferred to 
another vessel in which it is weighed by itself with scales con- 
structed to weigh such small weights with accuracy ; or the 
coil is removed and weighed with the contained water. In the 



* Correction made only for coil calorimeter to be described. 



STEAM-BOILER TRIALS. 52$ 

former case, drops of water may adhere to the Internal surfaces 
of the coil and escape measurement ; in the latter, the weight 
to be determmed is increased by the known weight of the coil, 
and less delicacy of w^eighing becomes possible. 

The following is Kent's description of his calorimeter, which 
is of this class, and has been found to give good results : "'^ 

A surface-condenser is made of light-weight copper tubing 
f ^ in diameter and about 50' in length, coiled into two coils, 
one inside of the other, the outer coil 14'' and the inner lo'^ in 
diameter, both coils being 15^^ high. The lower ends of the 
coils are connected by means of a brazed T-coupling to a shorter 
coil, about 5' long, of 2'^ copper tubing, which is placed at the 
bottom of the smaller coil and acts as a receiver to contain the 
condensed water. The larger coil is brazed to a f pipe, which 
passes upward alongside of the outer coil to just above the level 
of the top of the coil and ends in a globe-valve, and a short 
elbow-pipe which points outward from the coil. The upper 
ends of the two f coils are brazed together into a T, and con- 
nected thereby to a |'^ vertical pipe provided with a globe-valve, 
immediately above which is placed a three-way cock, and above 
that a brass union ground steam-tight. The upper portion of 
the union is connected to the steam-hose, which latter is 
thoroughly felted down to the union. The three-way cock has 
a piece of pipe a few inches long attached to its middle outlet 
and pointing outward from the coil. 

A water-barrel, large enough to receive the coil and with 
some space to spare, is lined with a cylindrical vessel of galva- 
nized iron. The space between the iron and the wood of the 
barrel is filled with hair-felt. The iron lining is made to return 
over the edge of the barrel, and is nailed down to the outer 
edge so as to keep the felt always dry. The barrel is furnished 
also with a small propeller, the shaft of which runs inside of 
the inner coil when the latter is placed in the barrel. The 
barrel is hung on trunnions by a bail by which it may be 
raised for weighing on a steelyard supported on a tripod and 
lifting lever. The steelyard for weighing the barrel is graduated 

* Trans. Am. Soc. M. E. 1884. 



526 THE STEAM-BOILEK. 

to tenths of a pound, and a smaller steelyard is used for weigh- 
ing the coil, which is graduated to hundredths of a pound. 

In operation, the coil, thoroughly dry inside and out, is 
carefully weighed on the small steelyard. It is then placed in 
the barrel, which is filled with cold water up to the level of the 
top of the globe-valves of the coil and just below the level of the 
three-way cock, the propeller being inserted and its handle con- 
nected. The barrel and its contents are carefully weighed on 
the large steelyard ; the steam-hose is connected by means of 
its union to the coil, and the three-way cock turned so as to let 
the steam flow through it into the outer air, by which means 
the hose is thoroughly heated ; but no steam is allow^ed to go 
into the coil. The water in the barrel is now rapidly stirred in 
reverse directions by the propeller and its temperature taken. 
The three-way cock is then quickly turned, so as to stop the 
steam escaping into the air and to turn it into the coil ; the 
thermometer is held in the barrel, and the water stirred until 
the thermometer indicates from five to ten degrees less than the 
maximum temperature desired. The globe-valve leading to the 
coil is then rapidly and tightly closed, the three-way cock turned 
to let the steam in the hose escape into the air, and the steam 
entering the hose shut off. During this time the water is being 
stirred, and the observer carefully notes the thermometer until 
the maximum temperature is reached, which is recorded as the 
final temperature of the condensing water. The union is then 
disconnected and the barrel and coil weighed together on the 
large steelyard ; the coil is then withdrawn from the barrel and 
hung up to dry thoroughly on the outside. When dry it is 
weighed on the small scales. If the temperature of the water 
in the barrel is raised to iio° or 120° the coil will dry to con- 
stant weight in a few minutes. After the weight is taken, both 
globe-valves to the coil are opened, the steam-hose connected, 
and all of the condensed water blown out of the coil, and steam 
allowed to blow through the coil freely for a few seconds at 
full pressure. When the coil cools it may be weighed again, 
and is then ready for another test. 

If both steelyards were perfectly accurate, and there were 
no losses by leakage or evaporation, the difference between the 



STEAM-BOILER TRIALS, 52/ 

original and final weights of the barrel and contents should be 
exactly the same as the difference between the original and 
final weights of the coil. In practice this is rarely found to be 
the case, since there is a slight possible error in each weighing, 
which is larger in the weighing on the large steelyard. In 
making calculations the weights of the coil on the small steel- 
yard should be used, the weight on the large steelyard being 
used merely as a check against large errors. 

The late Mr. J. C. Hoadley constructed exceedingly accu- 
rate apparatus of the " coil " type and obtained excellent re- 
sults. 

It is evident that this Calorimeter maybe used continuously, 
if desired, instead of intermittently. In this case a continuous 
flow of condensing water into and out of the barrel must be 
established, and the temperature of inflow and outflow and of 
the condensed steam read at short intervals of time. 

264. The Continuous Calorimeter is an instrument in 
which the operations of transfer of steam to the instrument 
and its examination are not intermitted, as is necessarily the 
case in the more commonly employed forms of the apparatus. 
The instrument being thus kept in use continuously, every 
variation in the quality of steam can be observed and the num- 
ber of observations can be increased to any desired extent, and, 
the apparatus being accurate, any degree of exactness of mean 
results can be attained. 

•• One of the earliest forms of this instrument was devised by 
Mr. John D. Van Buren, of the U. S. N. Engineers, and In- 
structor in Engineering at the Naval Academy, about 1867. 
This instrument, as constructed by Mr. T. Skeel, and used by a 
committee of judges"^ at the exhibition of the American In- 
stitute, 1874-5, of which the Author was chairman, was made 
as follows : 

Steam was drawn from the steam-drum, near the safety- 
valve, through a felted pipe \\ inches (3.8 cm.) diameter, into a 
rectangular spiral or coil consisting of 80 feet (24.4 m.) of 
pipe of similar size. Condensing water from the street-main 
was led into the tank surrounding the coil or '* worm," and 

* Trans. Am. Inst. 1875; Van Nostrand's Mag. 1875. 



528 



THE STEAM-BOILER. 



issued at the bottom through a ''standard orifice," the rate of 
discharge from which had been determined and the law of its 
variation with change of head ascertained. The quantity of 
condensing water thus became known by observing the head 
of water within the tank. The water of condensation from the 
coil was caught in a convenient vessel, and weighed on scales 
provided for that purpose. The temperature of the condensing 
water at' entrance and exit was shown by fixed thermometers, 
and that of the water of condensation at its issue from the coil 
was similarly shown, while the steam-gauge placed on the boiler 
gave the other needed data. The calculations are evidently 
precisely the same as with the preceding type of calorimeter. 

TJie Barrus Calorimeter'^ (Fig- hq) is essentially of a small 
surface-condenser. The steam enters by the pipe 7'. The con- 

densing-surface, a^ is a continua- 
tion and enlargement of the 
supply-pipe, a i-inch (2.54 cm.) 
iron pipe with a length of 12 
inches (30.4 cm.) of exposed sur- 
face. This pipe is under the full 
pressure of steam. The con- 
densed water collects in the lower 
parts of the apparatus, where its 
level is shown in the glass, <?, and 
is drawn off by means of the 
valve, d. The injection-water, 
cooled to a temperature of 40° 
Fahr., or less, enters the wooden 
vessel, 0, through the valve, b^ 
and circulates around the con- 
densing pipe, carried downward 

Fig. 119.— The Continuous Calorimeter, ^q the bottom by mcanS of the 

tube k, and overflows at the pipe, c, after passing through the 
mixing chambers, m. The amount of water admitted is regu- 
lated so as to secure a temperature at the overflow of 75° or 80° 
Fahr., or the approximate temperature of the surrounding 
atmosphere. The thermometers, / and g, which are read to 




* Trans. Am. Soc. M. E. 1884. 



STEAM-BOILER TRIALS. 529 

tenths of a degree, show the temperature of injection and over- 
flow water, and the thermometer, //, shows that of the con- 
densed water. The overflow water and the condensed water 
are collected in a system of weighing tanks. The steam-pipe 
down to the surface of the water, and the pipes in the lower 
part of the apparatus, are covered with felt. 

There is no wire-drawing of the steam, and no allowance to 
be made for specific heat of the apparatus. The only correc- 
tion to be made of material amount is for radiation from the 
pipes covered with felt, and this can be accurately determined 
by an independent radiation experiment, made when the con- 
denser vessel is empty. 

Another form of instrument devised by the same engineer 
is arranged in such manner as to permit the steam from the 
boiler to be dried and the quantity of heat so employed meas- 
ured as a gauge of the amount of water contained in the steam. 
This form of this apparatus is found very satisfactory.'^ 

The pipe conveying the steam to be tested is usually 
a half-inch (1.27 cm.) iron pipe. A long thread is cut on this 
pipe, and it is screwed into the main steam supply-pipe 
of the boiler in such a manner as to extend diametrically 
across to the opposite side. The inclosed part is perforated 
with from 40 to 50 small holes, and the open end of the 
pipe sealed. If the pipe is screwed into the under side 
the perforations begin at a distance of one inch (2.54 cm.) 
from the bottom. The connection is made as short as 
possible, and covered with felt. Where the calorimeter caa 
be attached to the under side of the main, the distance to 
the top valve need not exceed six inches (15 cm.). In this 
position it is self-supporting. The steam for the superheater 
is also supplied by a half-inch iron pipe, but this may be at- 
tached to the main at any convenient point. 

Steam to be tested enters by the pipe, which has a 
jacket. On passing out the thermometer gives its tem- 
perature, and it is discharged through a small orifice \ inch 
(0.32 cm.) in diameter. Steam to be superheated enters 
and is superheated by a gas-lamp, passes the thermometer,, 

* Trans. Am. Soc. Mach. Engrs., vol. vii. p. 178. 
34 



530 



THE STEAM-BOILER. 



and issues through an opening Hke that for the steam. The 
thermometers are immersed in oil-wells surrounded by the 
current of steam to be tested, or of that used in drying the 
boiler-steam. 

In the operation of this calorimeter steam at full pressure 
enters the apparatus, and the jacket-steam is heated until 
a perceptible rise of temperature above that due the pres- 
sure indicates that its moisture has been evaporated. The 
working having become steady, the difference between the 
temperatures is noted and corrected by deducting the ex- 
cess above that of moist steam at the observed pressure, 
and the number of degrees of superheating thus determined, as 
the rate of flow is the same from both orifices. Here the 
evaporation of one per cent of moisture from steam at 80 
pounds pressure (5.6 kilogs. per sq. cm.) reduces the tempera- 
ture of superheated steam about i8°.7 Fahr. (io°.4 Cent.), 
and the percentage of moisture is obtained by dividing the 
range of superheat, as above, by this number, or generally by 
the quotient of the latent heat at the observed pressure by 
47.5. The following are data and results obtained by the use 
of this apparatus : 

Data and Results in Full of Calorimeter Tests, 



£ 

^ 


Date. 


Gauge- 
pressure. 




11 

OJ 

m 


(U t« 

It 

° a 

(U U2 
111 


Number of degrees 
lost by superheated 
steam due to radi- 
ation from calorime- 
ter. 


Number of degrees 
representing radia- 
tion from supply- 
pipe. 


Amount of 

Moisture in the 

Wet Steam. 


Pi 

i 

e 






I 
2 
3 
4 

5 

6 
7 


Apr. 13 
" 14 
" 15 
" 16 
" 30 

May 4 
" 5 


89. 
89. 
86. 
86. 
85. 
80. 
84. 


99. 

75- 
74- 
74. 
72. 

77.5 
68. 


54.5 

37- 

37- 

39- 

38. 

41-5 

36.5 


8. 
5-5 
7- 
9-5 
10.5 
9-5 
6.5 


8. 

8. 

10.5 

7- 
8. 
8. 
7-5 


9-5 
9-5 
9-5 
9-5 
9-5 
9-5 
9-5 


19 
16. 
ID. 

9- 
6. 

9- 

8. 


1.02 
0.86 

0.54 
0.49 
0.32 
0.49 
0.43 



Note. — The duration of each of these tests was about one hour. 



* Obtained by dividing the preceding column by 18.6, the number of degrees 
corresponding to i per cent of moisture. 



STEAM-BOILER TRIALS. 



531 



Many other forms of calorimeter have been devised, but 
space will not permit their description. 

2^5. The Analysis of Gases* issuing from the furnace 
and passing up the chimney is sometimes an important detail 
of the work of testing a steam-boiler. Such an investigation 
involves only an operation of great simplicity which can easily 
be performed by any engineer. If it is not found convenient 
to make the analysis in the office of the engineer, he can have 
the work done, at little expense, by a chemist of known skill 
and reliability. It is only by a knowledge of the proportions 
of constituents of the flue-gases that it can be determined 
whether the combustion is complete, whether the products of 
combustion are diluted with excess of air, and whether the fuel 
used has been so burned as to give its best effect. Such analyses 
also enable the engineer to ascertain the best method of burn- 
ing the fuel. 

In sampling the gases, a matter in regard to which some 
precaution is advisable, the 
method of Mr. Hoadley is found 
very satisfactory.! 

Very great diversities in 
composition often exist in the 
same flue at the same time. 
To obtain a sample, allow one 
orifice to draw off flue-gases 
for each 25 sq. inches (161 sq. 
cm.) of cross-section of flue. 
The pipes must be of equal 
diameter and of equal length. 
These should be secured in a 
box of galvanized sheet-iron, 
equal in thickness to one course 

of brick, so that the ends may be evenly distributed over the 
flue A (Fig. 120), and their other open ends inclosed in the 




Fig. 120. — Flue-gas Sampling. 



* Consult Handbook of Gas Analysis, by C. Winkler. 
Voorst. 1885. 

f Trans. Am. Soc. M. E., vol. vi. 



London : J. Van 



532 THE STEAM-BOILER. 

receiver B. If the flue gases be drawn off from the receiver 
B by four tubes C C, into a mixing box D, beneath, a good 
mixture can be obtained. 

The sampling of the gas should be carried out at intervals 
of 10 to 15 minutes throughout the trial. The gas should be 
received in an air-tight pipe or jar. The composition of the 
gases should be determined as far as regards carbonic acid, car- 
bonic oxide, and oxygen. The tube should be of porcelain or 
glass for very hot flues, since iron tubes at such temperatures 
are oxidized. Supposing an analysis of the gas give K per 
cent of carbonic acid, O per cent of oxygen, and N per cent of 
nitrogen, then the proportion of air actually used to the 
theoretical quantity required is \ to x. 



Where 



N 21 



X = — or 



79 O' 

N-^^0 21-79^ 

unity of weight of this coal will then give, at a temperature of 
0° and a pressure of one atmosphere, 

C = carbonic acid : 

KO 

—- = oxygen: 

KN 

-—^ — nitrogen. 

The quantity of moisture in the escaping gases may be cal- 
culated from the moisture in the coal, from that formed by 
burning the hydrogen, and from that contained in the air ad- 
mitted to the furnace where the latter has been determined. 
Any serious break in the setting can be detected by filling 
the grate with smoky coal and then closing the damper. 

The apparatus designed by Professor Elliott, and employed 
in work carried on under the direction of the Author, consists, 



STEAM-BOILER TRIALS. 



533 



glass 




Fig. 121.— Apparatus for 



as shown in Fig. 121, .of two vertical 
joined by rubber-tubing, E^ at their upper 
ends. The large tube, AB, is the treating, 
the smaller, A' B' , the measuring tube; the 
^atter is suitably graduated to cubic centi- 
metres. Water-bottles, K, L, are connected 
with the lower ends of the tubes by tubing, 
NO, N'0\ and are used in effecting transfer of 
the gas from tube to tube. J/ is a funnel 
through which the reagents used may be in- 
troduced. G, F, and / are cocks of suitable 
size and construction. Gas analysis. 

In filling the apparatus it is set up conveniently near the 
flue, and the line of tubing from the collector, within the latter, 
is connected with the tube AB. The receiver L being de- 
tached the lower end of AB is connected with an aspirator or 
equivalent apparatus, such, for example, as might be improvised 
by the use of an air-tight tank or a barrel ; and the flow thus 
produced, when the aspirator is emptied of its water, fills the 
tube AB with gas drawn from the flue. It is retained by clos- 
ing the valves i^and /, which had been open during the opera- 
tion, of ^ filling. The tube is then disconnected from the aspi- 
rator, and the receiver, or bottle, Z, connected as shown, and in 
such manner that no air can reach the tube AB. 

Removing the apparatus to the laboratory or other con- 
venient location, the analysis is made as follows : 

Pass into A'B' a convenient volume, as 100 c.c. of the gas, 
and discharge the remainder through the valve and funnel F 
and M, filling the tube AB with water from L. Transfer the 
measured gas back to AB, through E, and add a solution from 
M, which will absorb some one constituent. Return the gas to 
A'B', and again read its volumes. The difference is the quan- 
tity of gas absorbed. Repeat this process, using next an ab- 
sorbent which will take up a second constituent of the gas, and 
thus obtain a second measure of volume ; and thus continue until 
all the desired determinations are made. All readings should 
be made at the same temperature, or practically so. The tube 



534 THE STEAM-BOILER. 

AB should be well washed at each operation, in order that no 
reagent should be affected by traces of that previously used. 

The absorbents employed are best taken in the following- 
order: 

1. Caustic potash — to absorb carbonic acid. 

2. Potassium pyrogallate — to absorb free oxygen. 

3. Cuprous chloride in concentrated hydrochloric-acid solu- 
tion — to absorb carbonic oxide. 

After their use nitrogen will remain, and will be measured 
as a balance which, added to the sum of the measured volumes 
of gases absorbed, should give the original total. Where 
weights are to be determined, the volumetric measures ob- 
tained as above are to be reduced by the usual process. 

The atomic weights of the principal constituents being, 
oxygen, 16; nitrogen, 14; carbon monoxide, 28; carbon dioxide, 
44, we shall have by percentages, where the symbols represent 
per cent in volumes, for each, when the total is 

M = 14N+ 16O + 2SCO + 44CO,y 



14N 16O 2SCO 44CO, . , 

-M^ -M^ -W^ -^-, respectively. 



32 
Since the total per cent of oxygen is measured by — CO^ -|- 

—^CO -\- free oxygen, and the total per cent of carbon is —CO^ 

12 

-\ qCO^ we shall have for the percentage of each, 

2o 



_ 32 X 44 X CO^ 16 X 28 X CO 16O 

^ — ^ ^ n/r \ ^Q 7\/r \ 



^M ' 28i^ ' M ' 



_ 12 X 44 X CO , 12 X 28 X ^(9 

^ — . . n/r 1 



44J/ ' 2%M 



J 



STEAM-BOILER TRIALS. 535 

or. 



^ - ^- M ^ M 






The total oxygen is that which entered the furnace as the 
supporter of combustion, and is a measure- of the air supplied. 
The ratio of free to combined oxygen is a measure of the ratio 
of the air acting as a diluent simply to that supporting com- 
bustion. 

Thus these measurements exhibit the efBciency of combus- 
tion, the quantity of air employed, and the magnitude of the 
wastes of heat at the chimney, occurring through imperfect 
combustion or excess of air-supply. It is evident, however, 
that where moisture or steam accompanies the gases, it escapes 
measurement ; this, however, introduces no important error in 
ordinary work. 

266. Efficiency of Combustion is indicated by the analysis 
of the flue-gases with very great certainty. The appearance of 
carbon monoxide at the chimney proves the combustion to be 
imperfect in proportion as it is more or less abundant. The 
presence of unconsumed oxygen, on the other hand, in the ab- 
sence of carbon monoxide, proves an excess of air-supply. 
Both gases appearing is a proof of incomplete intermixture of 
air and combustible, or of so low a temperature of furnace as to 
check combustion. This analysis being compared with that of 
the fuel reveals the character and the perfection of combus- 
tion, and permits a very exact determination to be made of the 
specific heat of the gases, and is thus a check on calculations 
of wasted heat. 

267. Draught-gauges are made for the purpose of deter- 
mining the head-producing draught and the intensity of the 
draught, which are of many forms, but which usually depend 
upon the measurement of the head of water which balances 
that head at the chimney. A very compact and accurate form 



536 



THE STEAM-BOILER. 



of draught-gauge, used by the Author with very satisfactory 
results, is that of Mr. J. M. Allen (Fig. 122). 

A and A' are glass tubes, mounted as shown, communicating 
with each other by a passage through the base, which may be 
closed by means of the stop-cock shown. Surrounding the 
glass tubes are two brass rings, B and B' . These rings are 
attached to blocks which slide in dovetailed grooves in the 




lit'- ■■■ .;,V F F' 

Fig. 122. — Draught-gauge. 



body of the instrument, and may be moved up and down 
by screws at F F . The scales are divided into fortieths of 
an inch, and read to thousandths of an inch by the verniers 
e and e\ which are attached to the sliding rings B B' . If the 
two short rings are set at different heights, the difference in 
readings will give the difference of level. The thermometer is 
for the purpose of noting the temperature of the external air. 
The method of using the instrument is as follows i"^ At a con- 

* I'he Locomotive, May, 1884, p. 67. 



STEAM-BOILER TRIALS. 



537 



venient point near the base of the chimney a hole is made 
large enough to insert a thermometer. The height from this 
opening to the top of chimney, and also of grates, should be 
noted. The chimney-gauge is attached to some convenient 
wall. The tubes are filled about half full of water, when the 
verniers afford an easy means of setting it perpendicular. One 
end of a flexible rubber tube is then inserted into the upper 
end of one of the glass tubes, and the other end of the tube is 
in the chimney-flue. The tubes B B' are adjusted until their 
upper ends are just tangent to the surface of the water in the 
two tubes. The reading of the two scales is then taken, and 
their difference. At the same time the temperature of the 
flue is noted, as well as that of the external atmosphere. Com- 
parison may then be made with the following table, computed 
for use in this connection for a chimney lOO feet high, with 
various temperatures outside and inside of the flue, and on the 
supposition that the temperature of the chimney is uniform 
from top to bottom — an inaccurate though usual assumption, 
however. For other heights than lOO feet, the theoretical 
height is found by simple proportion, thus : Suppose the exter- 
nal temperature is 60°, temperature of flue 380°, height of 
chimney 137 feet, then under 60° at the top of the table, and 
opposite to 380° interpolated in the left-hand margin, we 
find .52''. 

Then 100 : 137 :: .^2" : .J\" , which is the required height 
for a 137-foot chimney, and similarly for any other height. 



HEIGHT OF WATER COLUMN DUE TO UNBALANCED PRESSURE IN 
CHIMNEY 100 FEET HIGH. 



Temperature 


Temperature (Fahr.) of 


THE External Air— Barometer, 14.7. 


in the 










Chimney. 












Fahr. 


30° 


40° 


60° 


80° 


100» 


220 


419 


•355 


.298 


.244 


.192 


250 


468 




405 


.347 


.294 


.242 


300 


541 




478 


.420 


.367 


.315 


350 


607 




543 


.486 


•432 


.380 


400 


662 




598 


•541 


.488 


•436 


450 


714 




651 


•593 


•540 


.488 


500 


760 




697 


•639 


.586 


•534 



CHAPTER XV. 

STEAM-BOILER EXPLOSIONS * 

268. Steam-boiler Explosions are among the most terrible 
and disastrous of all the many kinds of accident, the introduc- 
tion of which has marked the advancement of civilization and 
its material progress. Introduced by Captain Savery at the 
beginning of the i8th century with the first attempts to apply 
steam-power to useful purposes, they have increased in fre- 
quency and in their destructiveness of life and property con- 
tinually, with increasing steam-pressures and the unintermitted 
growth of these magazines of stored energy, until to-day the 
amount of available energy so held in control, and liable at 
times to break loose, is often as much as two or even three 
millions of foot-pounds (276,500 to 414,760 kilogrammetres), 
and sufficient to raise the enclosing vessel 10,000 or even 20,000 
feet (3048 to 6096 m.) into the air, the fluid having a total 
energy, pound for pound, only comparable with that of gun- 
powder. 

In this and the following article it is proposed to present 
the results of a series of calculations relating to the magnitude 
of the available energy contained in masses of steam and of 
water in steam-boilers. This energy has been seen to be meas- 
ured by the amount of work which may be obtained by the 
gradual reduction of the temperature of the mass to that due 
atmospheric pressure by continuous expansion. 

The subject is one which has often attracted the attention 
of both the man of science and the engineer. Its importance, 
both from the standpoint of pure science and from that of 
science applied in engineering and the minor arts, is such as 

* This chapter has been separately printed with slight modifications as a 
monograph "On Steam-boiler Explosions," and published by the Messrs. 

Wiley. 



STEAM-BOILER EXPLOSIONS. 539 

would justify the expenditure of vastly more time and atten- 
tion than has yet ever been given it. Mr. Airy * and Professor 
Rankine f published papers on this subject in the same number 
of i\\Q Pliiiosophical Magazine {^ow. 1863), the one dated the 
3d September and the other the 5th October of that year. 
The former had already presented an abstract of his work at the 
meeting of the British Association of that year. 

In the first of these papers it is remarked that " very little 
of the destructive effect of an explosion is due to the steam 
which is confined in the steam-chamber at the moment of the 
explosion. The rupture of the boiler is due to the expansive 
power common at the moment to the steam and the water, both 
at a temperature higher than the boiling-point ; but as soon as 
the steam escapes, and thereby diminishes the compressive 
force upon the water, a new issue of steam takes place from the 
water, reducing its temperature ; when this escapes, and further 
diminishes the compressive force, another issue of steam of 
lower elastic force from the water takes place, again reducing 
its temperature : and so on, till at length the temperature of 
the water is reduced to the atmospheric boiling-point, and the 
pressure of the steam (or rather the excess of steam-pressure 
over atmospheric pressure) is reduced to o." 

Thus it is shown that it is the enormous quantity of steam 
so produced from the water, during this continuous but exceed- 
ingly rapid operation, that produces the destructive effect of 
steam-boiler explosions. The action of the steam which may 
happen to be present in the steam-space at the instant of rupture 
is considered unimportant. 

Mr. Airy had, as early as 1849, endeavored to determine the 
magnitude of the effect thus capable of being produced, but had 
been unable to do so in consequence of deficiency of data. His 
determinations, as published finally, were made at his request by 
Professor W. H. Miller. The data used are the results of the ex- 
periments of Regnault and of Fairbairn and Tate on the relations 
of pressure, volume, and temperature of steam, and of an experi- 

* ' ' Numerical Expression of the Destructive Energy in the Explosions of 
Steam-boilers." 

\ " On the Expansive Energy of Heated Water," 



540 THE STEAM-BOILER. 

ment by Mr. George Biddle, by which it was found that a locomo- 
tive boiler, at four atmospheres pressure, discharged one eighth 
of its liquid contents by the process of continuous vaporization 
above outlined, when, the fire being removed, the pressure was 
reduced to that of the atmosphere. The process of calculation 
assumes the steam so formed to be applied to do work expand- 
ing down to the boiling-point, in the operation. The work so 
done is compared with that of exploding gunpowder, and the 
conclusion finally reached is that " the destructive energy of one 
cubic foot of water, at a temperature which produces the pres- 
sure of 60 lbs. to the square inch, is equal to that of one pound 
of gunpowder." 

The work of Rankine is more exact and more complete, as 
well as of greater practical utility. The method adopted is that 
to be described presently, and involves the application of the 
formulas for the transformation of heat into work which had 
been ten years earlier derived by Rankine and by Clausius, inde- 
pendently. This paper would seem to have been brought out 
by the suggestion made by Airy at the meeting of the British 
Association. Rankine shows that the energy developed during 
this, which is an adiabatic method of expansion, depends solely 
upon the specific heat and the temperatures at the beginning 
and the end of the expansion, and has no dependence, in any 
manner, upon any other physical properties of the liquid. He 
then shows how the quantity of energy latent in heated water 
may be calculated, and gives, in illustration, the amount so de- 
termined for eight temperatures exceeding the boiling-point. 

This subject attracted the attention of the engineer at a very 
early date. Familiarity with the destructive effects of steam- 
boiler explosions, the singular mystery that has been supposed 
to surround their causes, the frequent calls made upon him, in 
the course of professional practice and of his studies, to exam- 
ine the subject and to give advice in matters relating to the use 
of steam, and many other hardly less controlling circumstances, 
invest this matter with an extraordinary interest. 

A steam-boiler is a vessel in which is confined a mass of 
water, and of steam, at a high temperature, and at a pressure 
greatly in excess of that of the surrounding atmosphere. The 



STEAM-BOILER EXPLOSIONS. 54 1 

sudden expansion of this mass from its initial pressure down to 
that of the external air, occurring against the resistance of its 
" shell " or other masses of matter, may develop a very great 
amount of work by the transformation of its heat into mechani- 
cal energy, and may cause, as daily occurring accidents remind 
us, an enormous destruction of life and property. The enclosed 
fluid consists, in most cases, of a small weight of steam and a 
great weight of water. In a boiler of a once common and still 
not uncommon marine type, the Author found the weight of 
steam to be less than 250 pounds, while the weight of water was 
nearly 40,000 pounds. As will be seen later, under such con- 
ditions, the quantity of energy stored in the water is vastly in 
excess of that contained in the steam, notwithstanding the fact 
that the amount of energy per unit of weight of fluid is enor- 
mously the greater in the steam. A pound of steam, at a pres- 
sure of six atmospheres (88.2 pounds per square inch), above 
zero of pressure, and at its normal temperature, 177 C. (319° F.), 
has stored in it about 75 British thermal units (32 calories), 
or nearly 70,000 foot-pounds of mechanical energy per unit of 
weight, in excess of that which it contains after expansion to 
atmospheric pressure. A pound of water accompanying that 
steam, and at the same pressure, has stored within it but about 
one tenth as much available energy. Nevertheless, the dispro- 
portion of weight of the two fluids is so much greater as to make 
the quantity of energy stored in the steam contained in the 
boiler quite insignificant in comparison with that contained in 
the water. These facts have been fully illustrated by the figures 
presented already. 

269. The Energy Stored in steam-boilers is capable of 
very exact computation by the methods already described, and 
the application of the results there reached gives figures that 
are quite sufficient to account for the most violently destruc- 
tive of all recorded cases of explosion. 

A steam-boiler is not only an apparatus by means of which 
the potential energy of chemical affinity is rendered actual 
and available, but it is also a storage-reservoir, or a magazine, 
in which a quantity of such energy is temporarily held ; and 
this quantity, always enormous, is directly proportional to the 



542 



THE STEAM-BOILER. 



weight of water and of steam which the boiler at the time con- 
tains. 

Comparing the energy of water and of steam in the steam- 
boiler with that of gunpowder, as used in ordnance, it has been 
found that at high pressures the former become possible rivals 
of the latter. The energy of gunpowder is somewhat variable, 
but it has been seen that a cubic foot of heated water, under a 
pressure of 60 or 70 pounds per square inch, has about the same 
energy as one pound of gunpowder. The gunpowder exploded 
has energy sufficient to raise, its own weight to a height of nearly 
50 miles, while the water has enough to raise its weight about 
one sixtieth that height. At a low red heat water has about 
40 times this latter amount of energy in a form to be so ex- 
pended. Steam, at 4 atmospheres pressure, yields about one 
third the energy of an equal weight of gunpowder. At 7 at- 
mospheres it has as much energy as two fifths of its own weight 
of powder, and at higher pressures its energy increases very 
slowly. 

Below are presented the weights of steam and of water con- 
tained in each of the more common forms of steam-boilers, th^ 
total and relative amounts of energy confined in each under the 
usual conditions of working in every-day practice, and their 
relative destructive power in case of explosion. 

In illustration of the results of application of the computa- 
tions which have been given in § 142, and for the purpose of 
obtaining some idea of the amount of destructive energy stored 
in steam-boilers of familiar forms, such as the engineer is con- 
stantly called upon to deal with, and such as the public are 
continually endangered by, the following table has been calcu- 
lated. This table is made up by Mr. C. A. Carr, U. S. N., 
from notes of dimensions of boilers designed or managed at 
various times by the Author, or in other ways having special 
interest to him. They include nearly all of the forms in com- 
mon use, and are representative of familiar and ordinary prac- 
tice. 

No. I is the common, simple, plain cylindrical boiler. It is 
often adopted when the cheapness of fuel or the impurity of 
the water supply renders it unadvisable to use the more com- 



S TEA M-B OILER EXPL O SIONS. 



543 





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544 



THE STEAM-BOILER. 



plex, though more efficient, kinds. It is the cheapest and 
simplest in form of all the boilers. The boiler here taken was 
designed by the Author many years ago for a mill so situated 
as to make this the best form for adoption, and for the reasons 
above given. It is thirty inches in diameter, thirty feet long, 
and is rated at ten H. P., although such a boiler is often forced 
up to double that capacity. The boiler weighs a little over a 
ton, and contains more than twice its weight of water. The 
water, at a temperature corresponding to that of steam at lOO 
pounds pressure per square inch, contains over 46,600,000 foot- 
pounds of available explosive energy, while the steam, which 
has but one fifth of one per cent of the weight of the water, 
stores about 700,000 foot-pounds, giving a total of 47,000,000 
foot-pounds, nearly, or sufficient to raise one pound nearly 
10,000 miles. This is sufficient to throw the boiler 19,000 feet 
high, or nearly four miles, and with an initial velocity of pro- 
jection of 1 100 feet per second. 

Comparing this with the succeeding cases, it is seen that 
this is the most destructive form of boiler on the whole list. 
Its simplicity and its strength of form make it an exceedingly 
safe boiler, so long as it is kept in good order and properly 
managed; but if, through phenomenal ignorance or reckless- 
ness on the part of proprietor or attendant, the boiler is ex- 
ploded, the consequences are usually exceptionally disastrous. 

No. 2 was a " Cornish" boiler designed by the Author, about 
i860, and set to be fired under the shell. It was 6 feet by 36, 
and contained a 36-inch flue. The shell and flue were both of 
iron f inch in thickness. The boiler was tested up to 60 
pounds, at which pressure the flue showed some indications of 
alteration of form. It was strengthened by stay-rings, and the 
boiler was worked at 30 pounds. The boiler contained about 
12 tons of water, weighed itself 'j^ tons, and the volume of 
steam in its steam-space weighed but 31^^ pounds. The stored 
available energies were about 57,600,000 foot-pounds, and about 
700,000 of foot-pounds in the water and steam, respectively, a 
total of nearly 60,000,000. This was sufficient to throw the 
boiler to the height of 3400 feet, or over three fifths of a mile. 

Comparing this with the preceding, it is seen that the intro- 



STEAM-BOILER EXPLOSIONS. 545 

duction of the single flue, of half the diameter of the boiler, 
and the reduced pressure, have reduced the relative destructive 
power to but little more than one sixth that of the preceding 
forrri. 

No. 3 is a ''two-flue" or Lancashire boiler, similar in form 
and in proportions to many in use on the steamboats plying on 
our Western rivers, and which have acquired a very unenviable 
reputation by their occasional display of energy when carelessly 
handled. That here taken in illustration was designed by the 
Author. 42 inches in diameter, with two 14-inch flues of f iron, 
and is here taken as working at a pressure, as permitted by law^ 
of 150 pounds per square inch. It is rated at 35 horse-power, 
but such a boiler is often driven far above this figure. The 
boiler contains about its own weight (3 tons) of water, and but 
37 pounds of steam. The stored available energy is 83,000,000 
foot-pounds, of which the steam contains but a little above five 
per cent. Its explosion would uncage sufficient energy to throw 
the boiler nearly 2\ miles high, with an initial velocity of 900 
feet per second. Both this boiler and the plain cylinder are 
thus seen to have a projectile effect only to be compared to 
that of ordnance. 

No. 4 is the common plain tubular boiler, substantially as 
designed by the Author at about the same time with those al- 
ready described. It is a favorite form of boiler, and deserv- 
edly so, with all makers and users of shell-boilers. That here 
taken is 60 inches in diameter, containing 66 3-inch tubes, and 
is 15 feet long. The specimen here chosen has 850 feet of 
heating and 30 feet of grate-surface, is rated at 60 horse-power,, 
but is oftener driven up to 75, weighs 9500 pounds, and contains 
nearly its own weight of water, but only 21 pounds of steam,. 
when under a pressure of 75 pounds per square inch, which is 
below its safe allowance. It stores 51,000,000 foot-pounds of 
energy, of which but 4 per cent is in the steam, and this is 
enough to drive the boiler just about one mile into the air, 
with an initial velocity of nearly 600 feet per second. The 
common upright tubular boiler may be classed with No. 4. 

Nos. 5-8 are locomotive boilers, of which drawings and 
35 



54^ THE STEAM-BOILER. 

weights were furnished by the builders. They are of different 
sizes, and both freight and passenger engines. The powers are 
probably rated low. They range from 1 5 to 50 square feet in area 
of grate, and from 875 to 1350 square feet of heating-surface. 
In weight the range is much less, running from 2|- to a little 
above 3 tons of water, and from 20 to 30 pounds of steam, as- 
suming all to carry 125 pounds pressure^ The boilers are seen 
to weigh from 2\ to 3 times as much as the water. These pro- 
portions differ considerably from those of the stationary boilers 
which have been already considered. The stored energy aver- 
ages about 70,000,000 foot-pounds, and the heights and veloci- 
ties of projection not far from 3000 and 500 feet ; although 
in one case they became nearly one mile and 550 feet, respec- 
tively. The total energy is only exceeded, among the stationary 
boilers, by the two flued boiler at 150 pounds pressure. 

Nos. 9 and 10 are marine boilers of the Scotch or "drum" 
form. These boilers have come into use by the usual j;i.!.ess 
of selection, with the gradual increase of steam-pressures oc- 
curring during the past generation as an accompaniment of the 
introduction of the compound engine and high ratios of expan- 
sion. The selected examples are designed for use in the 
new vessels of the U. S. Navy. The dimensions are obtained 
from the Navy Department, as figured by the Chief Draughts- 
man, Mr. Geo. B. Whiting. The first is that designed for the 
Nipsic, the second for the Despatch. They are of 300 and 
350 horse-power, and contain, respectively, 73,000,000 and 
110,000,000 of foot-pounds of available energy, or about 3000 
foot-pounds per pound of boiler, and sufficient to give a height 
and velocity of projection of 3000 and above 400 feet. These 
boilers are worked at a lower pressure than locomotive boilers ; 
but the pressure is gradually and constantly increasing from 
decade to decade, and the amount of explosive energy carried 
in our modern-steam vessels is now enormously greater than 
that of our locomotives, and in some cases already considerably 
exceeds that which they would carry were they supplied with 
boilers of the locomotive type and worked at locomotive pres- 
sures. The explosion of the locomotive boiler endangers com- 



STEAM-BOILER EXPLOSIONS. 547 

paratively few lives, and seldom does serious injury to property 
outside the engine itself. The explosion of one of these marine 
boilers while at sea would be likely to be destructive of many 
lives, if not of the vessel itself and all on board. 

Nos. II and 12 are boilers of the older types, such as are 
still to be seen in steamboats plying upon the Hudson and 
other of our rivers, and in Nev/ York harbor and bay. No. 1 1 
is a return-tubular boiler having a shell 10 feet in diameter by 
23 feet long, 2 furnaces each /f feet deep, 8 15-inch and 2 9-inch 
flues, and 85 return-tubes, a^\ inches by 15 feet. The boiler 
weighs 25 tons, contains nearly 20 tons of water and 70 pounds 
of steam, and at 30 pounds pressure stores 92,000,000 foot- 
pounds of available energy, of which 2-i- per cent resides in the 
steam. This is enough to hoist the boiler one third of a mile 
with a velocity of projection of 330 feet per second. The 
second of these two boilers is of the same weight, also of about 
200 horse-power, but carries a little more water and steam and 
stores 104,000,000 foot-pounds of energy, or enough to raise it 
1900 feet. This was a return-flue boiler, 33 feet long and hav- 
ing a shell 8f feet in diameter, flues 8|^ to 15 inches in diameter, 
according to location. 

The '•' sectional " boilers are here seen to have, for 250 horse- 
power each, weights ranging from about 35,000 to 55,000 
pounds, to contain from 15,000 to 30,000 pounds of water and 
from 25 to 58 pounds of steam, to store from 110,000,000 to 
230,000,000 foot-pounds of energy, equal to from 2000 to 5000 
foot-pounds per pound of boiler. The stored available energy 
is thus usually less than that of any of the other stationary 
boilers, and not very far from the amount stored, pound for 
pound, by the plain tubular boiler, the best of the older forms. 
It is evident that their admitted safety from destructive explo- 
sion does not come from this relation, however, but from the 
division of the contents into small portions, and especially from 
those details of construction which make it tolerably certain 
that any rupture shall be local. A violent explosion can only 
come of the general disruption of a boiler and the liberation at 
once of large masses of steam and water. 



548 



THE STEAM-BOILER 



270. The Energy of Steam alone, as stored in the boiler, 
is given by column 10 of the preceding table. It has been seen 
that it forms but a small and unimportant fraction of the total 
stored energy of the boiler. The next table exhibits the effect 
of this portion of the total energy, if considered as acting alone. 



STORED ENERGY IN THE STEAM-SPACE OF BOILERS. 



Type. 



Plain Cylinder 

Cornish 

Two-flue Cylinder, . . . 

Plain Tubular 

Locomotive 

Scotch Marine 

Flue and Return-tube 
Water-tube 





Stored in 






Steam 




Total Energy. 


(ft.-lbs.) 

per lb. of 

Boiler. 


Height of 
Projection. 


676,693 


271 


271 ft. 


709.310 


42 


42 " 


2,377.357 


351 


351 " 


1,022.731 


108 


108 " 


1.483.896 


76 


76 " 


2,135.802 


85 


85 " 


1,766,447 


86 


86 " 


1. 302. 431 


107 


107 " 


I 462.430 


54 


ii;: 


2,316,392 


61 


1-570,517 


28 


28 " 


1.643,854 


29 


29 " 


2,108.110 


61 


61 " 


3.5^3,830 


79 


79 '' 


1,311.377 


24 


24 " 



Initial 

Velocity 

per second. 



132 ft. 

32 '* 

150 '• 

83 - 

69 " 

74 " 

74 " 

83 " 

59 " 
62 ** 

42 " 

43 " 
59 " 
71 " 
39 " 



The study of this table is exceedingly interesting, if made 
with comparison of the figures already given, and with the facts 
stated above. It is seen that the height of projection, by the 
action of steam alone, under the most favorable circumstances, 
is not only small, insignificant indeed, in comparison with the 
height due the total stored energy of the boiler, but is proba- 
bly entirely too small to account for the terrific results of ex- 
plosions frequently taking place. The figures are those for the 
stored energy of steam in the working boiler ; they may be 
doubled, or even trebled, for cases of low water; they still 
remain, however, comparatively insignificant. 

The enormous power of molecular forces, even when heat 
is not added to reinforce them, is illustrated by the often de- 



STEAM-BOILER EXPLOSIONS. 



549 



scribed experiments of an artillery officer at Quebec"^ and others 
in which a large bombshell is filled 
with water, safely plugged, and 
exposed to low temperature. In 
such cases the expansive force ex- 
erted, when freezing, by the for- 
mation of ice and the increase of 
volume accompanying the forma- 
tion of the crystals, either drives 
out the plug, sometimes project- 
ing it hundreds of yards (Fig. 
123), or actually bursts the thick iron case. 

In the more familiar cases of purposely produced explosion, 
the expansion is caused by the production of great quantities 
of gas previously in Solid form. The violence of the familiar 
explosives as used in ordnance, in mining operations, is com- 




FlG. 



-Expansive Force of Ice. 




Fig. 124. — An Explosion. 

monly due to this combined effect of heat and chemical action, 
occurring by the sudden action of powerful forces. In the 
steam-boiler explosion mighty forces previously long held in 
subjection finally overcome all resistance, and their sudden ap- 
plication to external bodies constitutes the disaster. 

271. Explosion and Bursting are terms which, as often tech- 
nically used by the engineer, represent radically different phe- 
nomena. The explosion of a steam-boiler is a sudden and violent 



* Phenomena of Heat. Cazin. 



550 THE STEAM-BOILER. 

disruption, permitting the stored heat-energy of the enclosed 
water and steam to be expended in the enormously rapid ex- 
pansion of its own mass, and, often, in the projection of parts 
of the boiler in various directions, with such tremendous power 
as to cause as great destruction of life and property as if the 
explosion were that of a powder-magazine. The bursting of a 
boiler is commonly taken to be the rupture, locally, of the 
structure, by the yielding of its weakest part to a pressure 
which at the moment may not be deemed excessive, but which 
is too great for the weakened spot. The collapse of a flue is a 
form of rupture which is ordinarily considered as of the second 
class. With high steam-pressure, bursting or the collapse of a 
flue may occur with a loud report, and may even cause some 
displacement of the boiler ; but it is not generally termed an 
explosion when the boiler is simply ruptured, and is not torn 
into separated pieces. There is, however, no real boundary^ 
and the one grades into the other, with no defined line of de- 
marcation. 

It occasionally happens that an explosion takes place with 
such extraordinary violence and destructive effect that it has 
been thought best, especially by French writers, to class it by 
itself, and it is denoted a detonant or fulminant explosion, 
'''■ explosion fulminantey In such cases the report is like that 
of an enormous piece of ordnance ; the boiler is often rent into 
many parts, or even completely broken up, as if by dynamite ; 
and surrounding objects are destroyed as if by the discharge of 
a park of artillery. 

In any steam-boiler there may at any time exist a state 
of equilibrium between the resisting power of the boiler and 
the steam -pressure. In ordinary working, the latter is far 
within the former ; but as time passes the limiting condition 
is gradually approached, and in every explosion the line is 
passed. The pressure may rise until the limit of strength is at- 
tained, or the resisting power of the boiler may decrease to the 
limit : in either case the passage of the line is marked by ex- 
plosion, or a less serious method of yielding. 

272. The Causes of Boiler-explosions are numerous, but 
are usually perfectly well understood. Where uncertainty exists. 



STEAM-BOILER EXPLOSIONS. 551 

it is probably the fact that, were the cause ascertained, it would 
be found to be simple and well known. It is nevertheless true 
that some authorities, including a few experienced and distin- 
guished members of the engineering profession, believe that 
there are causes, at once obscure and of great potency and en- 
ergy, which are not yet satisfactorily understood. In this work 
the many causes to which explosions are, by various practi- 
tioners and writers, attributed may be divided into the known, 
the probable, the possible, the improbable, and the impossible 
and absurd. 

To the first class belong the general and fairly uniform 
weakness of boilers as compared with the steam-pressures car- 
ried ; the sticking of safety-valves, and the thousand and one 
other causes having their origin in the ignorance, the carelessness, 
or the utter recklessness of the designer, the builder, or the attend- 
ants intrusted with their management. To this class may be as- 
signed the causes of by far the greater proportion of all explo- 
sions ; and the Author has sometimes questioned whether this 
category may not cover absolutely all such catastrophes. To 
the second class may be assigned '^ low-water," a cause to which 
it was once customary to attribute nearly all explosions, but 
which is known to be seldom operative, and so seldom that 
some authorities now question the possibility of its action at 
all."^ Among the possible causes, acting rarely and under pe- 
culiar conditions, the Author would. place the overheating of 
water, and the storage of energy in excess of that in the liquid 
at the temperature due the existing pressure ; the too sudden 
opening of the throttle-valve or the safety-valve, producing 
priming and shock ; the spheroidal state of water ; and perhaps 
other phenomena. The improbable include the latter, however. 
The action of electricity — a favorite idea with the uninformed 
— may be taken as an example of the impossible and absurd. 
The actual causes of a vast majority of boiler-explosions are 
now determined by skiUed engineers, inspectors, and insurance 
experts ; and it is by them generally supposed that no so-called 
* mysterious" causes exist, in the sense that they are phenom- 

* See opinion of Mr. J. M. Allen, Sibley College Lecture, Sci. Am. Supple- 
fficnt, Feb. 19, 1887, p. 9272. 



552 THE STEAM-BOILER. 

ena beyond the present range of human knowledge and scien- 
tific investigation. 

All recent authorities agree in attributing boiler-explosions, 
almost without exception, to one or another of the following 
general classes of causes, and the Author is inclined to make no 
exception : 

(i) Defective design: resulting in weakness of shell, of 
flues, or of bracing or staying; in defective circulation; faulty 
arrangement of parts ; inefficiency of provision for supplying 
water or taking off steam ; and defects in arrangement leading 
to strains by unequal expansions, and other matters over which 
the designer has control. 

(2) Malconstruction : including choice of defective or im- 
proper material ; faulty workmanship ; failure to follow instruc- 
tions and drawings ; omission of stays or braces. 

(3) Decay of the structure with time or in consequence of 
lack of care in its preservation ; local defects due to the same 
cause or to some unobserved or concealed leakage while in 
operation. 

(4) Mismanagement in operation, giving rise to excessive 
pressure ; low water ; or the sudden throwing of feed-water on 
overheated surfaces: or the production of other dangerous 
conditions ; or failure to make sufficiently frequent inspection 
and test, and thus to keep watch of those defects which grow 
dangerous with time. 

Weakness of boiler or over-pressure of steam are the usual 
immediate causes of explosions. 

It has often been suggested that the most destructive boiler- 
explosions may be attributable to electricity, and may illustrate 
the effect of an unfamiliar form of lightning. Such hypotheses 
are, however, absurd. No storage and concentration of elec- 
tricity could be produced in a vessel composed of the best of 
conducting materials and enclosing a mass of fluid incapable of 
causing electrical currents, either great or small, under the con- 
ditions observed in the steam-boiler. The production of elec- 
tricity seen in Armstrong's experiments, a phenomenon some- 
times thought to support this theory, is simply the result of 
the friction of a moving jet of steam on the nozzle from which 



STEAM-BOILER EXPLOSIONS. 553 

It issued, and presents not the slightest reason for supposing 
that the electrical hypothesis of the origin of boiler-explosions 
has any basis of fact. 

Professor Faraday, in a report to the British Board of Trade, 
May, 1859, states his belief in the absurdity of the idea that 
the water within a steam-boiler may become decomposed, and 
the explosion of a mixture of gases so produced may burst a 
boiler: — " . . . . As respects the decomposition of the steam 
by the heated iron, and the separation of hydrogen, no new 
danger is incurred. Under extreme circumstances, the hydro- 
gen which could be evolved would be very small in quantity, 
would not exert greater expansive force than the steam, and 
would not be able to burn with explosion, and probably not at 
all, if it, with the steam, escaped through an aperture into the 
air or even into the fire-place." 

Decomposition cannot occur in the steam-boiler, ordinarily ; 
and if it were to happen in consequence of low-water and 
overheated plates, no oxygen could remain free to explosively 
combine with it. 

A half-century ago, M. Arago, in wTiting of steam-boiler 
explosions,^ asserted that " no cause of explosion exists which 
cannot be avoided by means at once simple and within reach 
of every one." A committee of the Franklin Institute, in 1830, 
asserted f of boiler-explosions that " they proceed, it is be- 
lieved, in most cases, from defective machinery, improper ar- 
rangement or distribution of parts, or, finally, from carelessness 
in management." These conclusions are fully justified by all 
later experience ; and it is now admitted by all accepted author- 
ities that a careful examination and study of the facts of the 
case will almost invariably enable the experienced engineer to 
determine the origin of the disaster. It follows that it is per- 
fectly practicable to so design, construct, and manage steam- 
boilers that there shall be absolutely no danger of explosion. 

273. The Statistics of Explosions have been very care- 
fully collected for many years in some European countries. 



* Mem. Roy. Acad. Sci. Inst. France, xxi. 
f Journal Franklin Institute, 1830. 



554 



THE STEAM-BOILER. 



notably in France, and are now given for the United States in 
very reliable form by inspectors, governmental and private, 
who are thoroughly familiar with the subject. The following 
is a list reported for the year 1885 : 

CLASSIFIED LIST OF BOILER-EXPLOSIONS. 





a 

a 


t 




1 

< 




c 

3 


^ 

3 


00 
<3 


6 

a 
en 


1 


I 


4> 

a 
1 


a 


1 




Saw-mills and wood-working 


5 


2 

4 


4 
2 


3 


3 
I 
I 

I 


2 
I 

I 

2 

I 


2 
I 

4 

I 
I 

I 


2 


3 
I 


4 
2 

3 

I 


I 
I 
2 

2 


2 

I 

4 
2 
I 


33 
10 


Locomotives • . • 


Steamboats, tugs, etc 

Portables, bolsters, and agri- 


2 


t6 


2 

3 

I 
I 


3 


t6 


Mines, oil wells, collieries, 
etc 


2 

I 
3 


5 


3 


2 


20 


Paper-mills, bleachers, digest- 


3 
10 


Rolling-mills and iron-works 

Distilleries, breweries, sugar- 
houses, dye-houses, ren- 
dering establishments, etc. 

Flour-mills and elevators... 

Textile manufactories 


2 

I 
3 


I 




3 


I 

I 
2 
I 

I 

12 

14 
6 


3 

I 


I 


4 
2 


2 

2 

I 


I 


... 


10 

I 






3 

20 

22 
30 


3 

14 

20 

28 


2 

7 

9 
9 


2 
12 

18 
32 








3 
14 

19 
40 


2 

15 

34 
22 


2 

17 

31 
21 


T« 


Total per month 

Persons killed— total 220— 


14 

24 

35 


10 

7 
21 


9 

II 
21 


II 

II 
13 


155 


Persons injured — total 288 — 
per month 









Boilers used in saw-mills are most frequently exploded, pre- 
sumably because of the cheapness of their construction, and 
the unskilfulness exhibited in their management ; boilers in 
mines are next in number of casualties. Mill-boilers explode 
with comparative infrequency. In the United States, accord- 
ing to the best estimates which the Author has been able to 
make, about one boiler in 10,000 explode among those which 
are regularly inspected and insured, and ten times that propor- 



STEAM-BOILER EXPLOSIONS. 



555 



tion among uninspected and uninsured boilers. In Great 
Britain, the proportion of explosions is much less than in the 
United States, the average number being less than one twentieth 
of one per cent, and the loss of life about three to every two 
explosions. In Great Britain, as in the United States and else- 
where, the majority of explosions are due to negligence. Ex- 
plosions might become almost unknown were a proper system 
of inspection and compulsory repair introduced. 

The returns of boiler-explosions in Great Britain and the 
United States show that not only in number but in destructive- 
ness the record of the United States always exceeds that of 
Great Britain, as is seen in the following tables : 





No. Explosions. 


No. Fatalities. 


No. Per's Inj'd. 


1884. 


1885. 


1884. 


1885. 


1884. 


1885. 


Great Britain . 
United States.. 


36 
152 


43 

155 


24 
254 


40 
220 


49 
261 


62 

288 





No. Explosions per 
Million Inhabitants. 


No. Fatalities per 
Explosion. 


1884. 


1885. 


1884. 


1885. 


Great Britain.. 
United States.. 


I 

3 


1. 17 
3-09 ■ 


.67 
1.67 


•93 
1.42 



The causes of the forty-three explosions in Great Britain 
are reported to have been : 



Cases. 

Deterioration or corrosion of boilers and safety-valves 20 

Defective design or construction of boiler or fittings 11 

Shortness of water 4 

Ignorance or neglect of attendants 4 

Miscellaneous 4 

Total 43 



556 



THE STEAM-BOILER. 



For the United States there are estimated to have been 
dangerous cases classified thus : 



Causes. 


Whole No. 


Dangerous. 


Deterioration or corrosion of boilers and safety-valves. . 

Defective design or construction of boiler or fittings 

Shortness of water 


17.873 

15,895 

130 

6,404 

6,928 


1,727 

2,957 

56 

983 

1,403 


Ignorance or neglect of attendants 


Miscellaneous 





The following are two classified lists of defects and causes 
of dangerous conditions, where in one case over 6000 boilers 
and in the other above 4000 were inspected in one month :* 



CAUSES OF DANGER. 



Nature of Defects. 



Deposit of sediment 

Incrustation and scale 

Internal grooving 

Internal corrosion 

External corrosion 

Broken, loose, and defective braces and stays 

Defective settings 

Furnaces out of shape 

Fractured plates 

Burned plates 

Blistered plates 

Cases of defective riveting 

Defective heads 

Leakage around tube ends 

Leakage at seams 

Defective water-gauges 

Defective blow-offs 

Cases of deficiency of water 

Safety-valves overloaded 

Safety-valves defective in construction 

Defective pressure-gauges 

Boilers without pressure-gauges 

Defective hand-hole plates 

Defective hangers 

Defective fusible plugs 

Total 



>,453 



Whole No. 


Dangerous. 


458 


32 


630 


55 


20 


7 . 


155 


16 


346 


23 


205 


39 


178 


17 


248 


12 


123 


65 


89 


22 


254 


II 


1,649 


187 


30 


15 


974 


331 


574 


22 


163 


27 


30 


8 


5 


2 


29 


7 


42 


7 


238 


19 


4 





3 


3 


13 





I 






927 



The Locomotive, December, 1884 ; September, 1886. 



STEAM-BOILER EXPLOSIONS. 



557 



Nature of Defects. 



Cases of deposit of sediment 

Cases of incrustation and scale 

Cases of internal grooving 

Cases of internal corrosion 

Cases of external corrosion 

Broken and loose braces and stays. . . . 

Settings defective 

Furnaces out of shape 

Fractured plates 

Burned plates . 

Blistered plates 

Cases of defective riveting 

Defective heads 

Serious leakage around tube ends. . . . 

Serious leakage at seams 

Defective water-gauges 

Defective blow-offs 

Cases of deficiency of water 

Safety-valves overloaded 

Safety-valves defective in construction 

Pressure-gauges defective 

Boilers without pressure-gauges 

Total 




It is seen that many of these defects, all of which are danger- 
ous and liable to cause explosion, are of very variable frequency ; 
as, for example, defective riveting, which is more than twice 
as common in the first list as any other d'efect, but which 
stands number three in the second ; while other defects are of 
quite regular occurrence, as the presence of sediment and of 
scale, grooving and other corrosion, injured plates, and defective 
gauges. Sediment, oxidation, and defective workmanship 
are evidently the most prolific causes of danger; and unequal 
expansion, to which many of the reported cases of leakage are 
attributable, hardly less so. 

An inspection of these tables plainly shows that the causes 
of steam-boiler explosion are commonly perfectly simple, and 
are well understood ; and a person familiar with the subject 
usually wonders that explosions occur as infrequently as they 
do, where there are so many sources of danger, and where so little 
intelligence and care is exhibited in their design, construction, 
and operation. There are, however, some interesting phenom- 



55^ THE STEAM-BOILER. 

ena and some very ingenious theories as to method of libera- 
tion of the enormous stock of energy of which every boiler is a 
reservoir, to which attention may well be given. 

274. Theories and Methods of explosions due to other 
causes than simple increase of steam-pressure or decrease in 
strength of boiler, and of such accidents as are common and 
well understood, and produce the greater number of disasters 
of the class here studied, are as various as they are interesting. 
The vast majority of all boiler-explosions have been, as has been 
seen, found to be due to causes which are readily detected, and 
are the simplest and most obvious possible. Here and there, 
however, an explosion takes place which is so exceptionally vio- 
lent or which occurs under such unusual and singular conditions 
as to give rise to question whether some peculiar phenomenon is 
not concerned in bringing about so extraordinary a result. Nearly 
all explosions have been produced either by a gradual rise in 
pressure until the resisting power of the boiler has been 
exceeded and an extended rupture liberates the stored energy ; 
or by a gradual reduction of the strength of the structure, until 
at last it is insufficient to withstand the ordinary working pres-, 
sure, and a general yielding leads to the same result. Such 
cases require little comment and no explanation ; but the rare 
instances in which a sudden development of forces far in excess 
of those exhibited in regular working have been believed to 
have been observed have given rise to much speculation, to 
many ingenious theories, and to an immense amount of spec- 
ulation and misconception on the part of those who are unfa- 
miliar with science, and without experience in the operation of 
this class of apparatus. 

Explosions probably always occur from perfectly simple and 
easily comprehended causes, are always the result of either 
ignorance or carelessness, and are always preventable where 
intelligence and conscientiousness govern the design, the con- 
struction, and the management of the boiler. A well-designed 
boiler, properly proportioned for its work and to carry the 
working pressure, well built, of good material, and intelligently 
and carefully handled, has probably never been known to 
explode. Explosions probably never occur, with either a grad- 



STEAM-BOILER EXPLOSIONS. 559 

ually increasing pressure of steam or decreasing strength of 
boiler, unless the strength of the structure is quite uniform ; 
local weakness is a safety-valve which permits a "burst," and 
insures against that more general disruption which is called an 
^' explosion." A long line of weakened seam, an extended 
crack, or a considerable area of surface thinned by corrosion 
may lead to an explosion and a general breaking up of the 
whole apparatus ; but any minor defect, where its site is sur- 
rounded by strong parts, will not be likely to produce that 
result. 

TJic Method of Explosion is in the great majority of 
cases the opening of a small orifice at a point of minimum 
strength, with outrush of water or steam, or both ; the rapid 
extension of the rupture until it becomes so great and the 
operation is so sudden that, no time being given for the gradual 
discharge of the enclosed fluids, the boiler is torn violently 
apart by the internal unrelieved pressure and distributed in 
pieces, the number of which is determined by the character and 
extent of the lines or areas of weakness. 

275. Clark and Colburn's Theory of boiler-explosions 
has been accepted as a " working hypothesis" by many engineers, 
and has some apparent foundation in experimentally ascer- 
tained fact. This theory is attributed to Mr. Zerah Colburn f 
but was probably, as stated by Mr. Colburn himself, original 
with Mr. D. K. Clark, who suggests that a rupture initiated at 
the weakest part of a boiler, above or near the water-line, may 
be extended, and an explosion precipitated by the impact of a 
mass of water carried toward it by the sudden outrush of a 
large quantity of steam, precisely as the " water-hammer" ob- 
served so frequently in steam-pipes causes an occasional rup- 
ture of even a sound and strong pipe. In fact, many instances 
have been observed in which the rent thus presumed to have 
been produced has extended not only along lines of reduced 
section, but through solid iron of full thickness and of the best 
quality. It is thus that Mr. Clark would account for the shat- 



* Steam-boiler Explosions, Zerah Colburn. London: John Weale. i8fo. 



560 THE STEAM-BOILER. 

tering and the deformation of portions of the disrupted boiler, 
which are often the most striking and remarkable phenomena 
seen in such cases. 

Colburn suggests that the explosion, in such cases, although 
seemingly instantaneous, may actually be a succession of oper- 
ations, three or four at least, as the following : 

(i) The initial rupture under a pressure which may be and 
probably often is the regular working pressure ; or it may be an 
accidentally produced higher pressure ; the break taking place 
in or so near the steam-space that an immediate and extremely 
rapid discharge of steam and water may occur. 

(2) A consequent reduction of pressure in the boiler and so 
rapid that it may become considerable before the inertia of the 
mass of water will permit its movement. 

■(3) The sudden formation of steam in great quantity with- 
in the water, and the precipitation of heavy masses of water, 
with this steam, toward the opening, impinging upon adjacent 
parts of the boiler and breaking it open, causing large open- 
ings or extended rents. 

(4) The completion of the vaporization of the now liberated 
mass of water to such extent as the reduction of the tempera- 
ture may permit, and the expansion of the steam so formed, 
projecting the detached parts to distance depending on the ex- 
tent and rapidity of this action. 

This series of phenomena may evidently be the accompani- 
ment of any explosion, to whatever cause the initial rupture 
may be due. One circumstance lending probability to this 
theory is the rarity of explosions originating in the failure of 
" water-legs" or other parts situated far below the water-line. 
This occasionally happens, as was seen some time ago at Pitts- 
burg in the explosion of a vertical boiler caused by a crack in 
the water-leg ; but it is almost invariably observed that explo- 
sions occur where long lines of weakened metal, defective 
seams, or of " grooving" extend nearly or quite to the steam- 
space."^ A local defect well below the water-line would 



^ The Westfield explosion illustrates this case. Jour. Frank Inst. 1875. 



STEAM-BOILER EXPLOSIONS. 56 1 

usually simply act as a safety-valve, discharging the contents 
of the boiler without explosion. 

276. Corroboratory Evidence has been here and tliere 
found. Lawson's experiments, and those of others, as well as 
many accidental explosions, have supplied evidence somewhat 
but not absolutely corroboratory of the Clark and Colburn the- 
ory. Mr. D. T. Lawson having become convinced of the 
truth of the Clark and Colburn theory, further conceived the 
idea that the opening and sudden closing of the throttle or 
the safety-valve might cause precisely the same succession of 
phenomena, and lead to the explosion of boilers, the opening 
starting the current and the closing of the valve producing 
impact that may disrupt the boiler. To test the truth of his 
hypothesis, he made a number of experiments, and succeeded 
in exploding a new^ and strong boiler at a pressure far below 
that which it had immediately before safely borne. As .^, 
preventive, he proposed the introduction of a perforated 
sheet-iron diaphragm dividing the interior of the boiler at or 
near the water-line ; the expectation being that it would check 
the action described by Colburn and prevent that percussive 
effect to which explosion w^as attributed by him, and also that it 
w^ould be found to possess some other advantages. 

The experiments were made at Munhall, near Pittsburg, 
Pa., in March, 1882, the boiler being of the cylindrical variety 
30 inches {j6 cm.) in diameter and 6| feet (2.06 m.) in length, 
of iron ^^ inch (0.48 cm.) in thickness. Its strength was esti- 
mated at 430 pounds per square inch (28f atmos.). It was 
fitted with a diaphragm, as above described. 

After some preliminary tests, the following were made,* 
the valve being opened at intervals and suddenly closed again 
at the pressures given below, as taken from the log. A steam- 
gauge was attached to the boiler above and one below the dia- 
phragm. The boiler contained 18 inches of water. Steam 
was generated slowly, and when the pressure had reached 50 
pounds operating the discharge valve began with the following 
results : 



Report of U. S. Inspectors to the Secretary of the Treasury, March 23, 1882, 
36 



562 



THE STEAM-BOILER. 



W 





Steam-gauge above 


Stea!\i-gauge below tme 


Steam-pressure 


Diaphragm. 


Diaphragm. 


AT WHICH 

Discharge-valve 














WAS RAISED. 


Needle fell 


Needle rose 


Needle fell 


Needle rose 




below 


above 


below 


above 


Pounds. 


Pounds. 


Pounds, 


Pounds. 


Pounds. 


50 


7 


3 


3 


00 


•• 80 


10 


7 


4 


00 


100 


12 


7 


5 


3 


125 


15 


15 


8 


4 


150 


20 


20 


8 


7 


175 


15 


23 


10 


10 


200 


20 


20 


15 


00 


225 


30 


20 


12 


00 


230 


40 


30 


10 


00 


250 


25 


20 


10 


00 


275 


30 


25 


15 


00 


300 


40 


35 


15 


00 



When the pressure in the boiler reached 300 pounds to the 
square inch it was decided that the boiler had been sufficiently 
tested, and the boiler was emptied and inspected. The rivets, 
seams, and all the other parts of the boiler were examined, and 
no strain, rupture, or weakness was discovered. The diaphragm 
was then cut out, leaving the flanges riveted to the sides of the 
shell and across the heads. The boiler was then again tested 
with the following results : 



Steam- pressure 

at which 

Discharge-valve 

was raised. 


Steam-gauge attached 

TO THE Boiler 

IN THE Steam-space. 


Steam-gauge attached 
TO Boiler in Water- 
space. 


Needle fell 
below 


Needle rose 
above 


Needle fell 
below 


Needle rose 
above 


Pounds. 


Pounds. 


Pounds. 


Pounds. 


Pounds. 


100 


3 


00 


3 


00 


125 
150 
175 
200 


2 

5 
4 
5 


00 

00 

2 

00 


3 
5 
3 

5 


00 

00 

2 

00 


210 


3 


00 


3 


00 


225 
235 


5 
Exploded. 


00 


3 


00 



When the discharge-valve was opened at 235 pounds pressure 
it caused the explosion of the boiler. It was blown into frag- 



STEAM-BOILER EXPLOSIONS. 5^3 

ments. The iron was torn and twisted into every conceivable 
shape ; strips of various sizes and proportions were found in all 
directions. The boiler did not always tear at the seams, but 
principally in the solid parts of the iron. At the time of the 
explosion the water-line was higher than during the test imme- 
diately preceding. At an earlier privately made experiment, as 
reported by the same investigator, an explosion of a' new boiler 
had been similarly produced at one half the pressure which it 
had been estimated that the boiler might sustain. A significant 
fact exhibited in the record is the enormously greater fluctua- 
tion of pressure in the boiler during the first than during the 
second trial, and the difference in the amount of that fluctuation 
above and below the diaphragm. 

The result of this action in the ordinary operation of the 
safety-valve or of the throttle-valve is apparently extremely un- 
certain. Many explosions have occurred under such circum- 
stances as would seem to indicate the probability of the action 
above described having been their cause, the disaster following 
the opening of safety-valves, or of the throttle at starting the 
engine. 

On the other hand, these operations are of constant occur- 
rence, and with weak and dangerous boilers, yet such explo- 
sions are known to be extremely rare. The Author, while offi- 
cially engaged in attempting the experimental production of 
boiler-explosions, as a member of the U. S. Board appointed 
for that purpose, made numerous experiments of this nature, 
but never succeeded in producing an explosion. The danger 
would seem to be, fortunately, less than it might be, judged 
from the above. The introduction of feed-water into the 
steam-space of boilers, producing sudden removal of pressure 
from the surface of the water, is sometimes supposed to have 
caused explosions. The explosion of a battery of several boil- 
ers simultaneously— not an infrequent case — is supposed to be 
attributable to the action described above, following the rup- 
ture of some one of the set. 

That this action can have more than a slight effect, and that 
it can do more than accelerate the rupture of a weak boiler and 



564 THE STEAM-BOILER. 

intensify the effects of explosions due to the action of other 
phenomena, remains to be proven by further investigation. 

Mr. J. G. Heaffman, writing in 1867,'^ anticipated Mr. Law- 
son's idea, and, after describing an explosion of a bleaching- 
boiler, to which the steam was supplied from a separate steam- 
boiler, attributes the catastrophe to impact of water against the 
shell on the accidental production of an opening at the man- 
hole, and asserts that explosions thus occur, not only from ex- 
cess of pressure, but also from shock. He further states that, 
in accordance with a request made by the Association of Ger- 
man Engineers, a commission of the Breslau Association, ex- 
perimenting with a small glass boiler, found that when the 
escape-pipes are only gradually opened, and the steam allowed 
gradually to escape, the generation of steam quietly continues 
and the water remains tranquil. But if the valve is quickly 
opened, steam-bubbles suddenly form all through the water, 
and rising to the surface, produce violent commotion. In one 
of these experiments it was his duty to watch the manometer, 
while another person quickly opened the valve to allow the 
steam to escape. As soon as the valve was opened the pres-. 
sure fell 3 pounds, but immediately again began to rise, and the 
boiler exploded. Where it had been in contact with the water 
it was shattered to powder, which lay around hke fine sand. Of 
the entire boiler only a few small pieces of the size of a dollar 
were left. Afterwards they constructed a similar glass boiler, 
with a cylinder 7 inches in diameter and 9 inches in length, 
and to the ends metal heads were fastened ; in the heads were 
pipes for leading in the steam. By means of a force-pump the 
boiler was filled with boiling water, the valve being left open 
meanwhile, in order that its sides might become evenly heated. 
Then half the water was drawn off, and air let in, and after- 
wards more boiling water forced in, so that the air was com- 
pressed, until the boiler exploded at a pressure of 15 atmos- 
pheres. 

The report was not nearly as loud as at the former explo- 
sion, which took place at a pressure of only three atmospheres, 

* Journal of Assoc, of German Engineers, 1867 ; Iron Age, 1867. 



STEAM-BOILER EXPLOSIONS. 565 

and the glass was only broken into several pieces. This, Mr. 
Heaffman considers, proves that the action of the water on the 
boiler is such as would be produced by exploding nitro-glycer- 
ine in the water. He goes on to state that in bleacheries, dye- 
Avorks, etc., the habit often prevails of suddenly opening the 
steam-cocks, thus endangering the boiler. 

He does not assert that every time a cock is suddenly 
opened an explosion must follow ; but that it may take place, 
experience has shown. In the experiments above described 
they had many times opened the glass boiler without causing 
an explosion ; with the second boiler, too, they had done so 
without being able to bring about explosion, both with high 
and low pressure. In the former class of explosions the 
steam shatters, twists, and contorts everything in an instant. 

" Water-hammer' has, by the bursting of steam-pipes, by a 
process somewhat closely related to that described by Clark 
and Colburn, sometimes caused fatal injury to those near at 
the instant of the accident. This is a phenomenon which has 
long been familiar to engineers, and the author has been cog- 
nizant of many illustrations, in his own experience, of its 
remarkable effects, and has sometimes known of almost as seri- 
ous losses of life as from boiler-explosions. It is rarely the 
cause of serious loss of property. 

When a pipe contains steam under pressure, and has intro- 
duced into it a body of cold water, or when a cold pipe con- 
taining water is suddenly filled w^th steam, the contact of the 
two fluids, even when the water is in very small quantities, 
results in a sudden condensation which is accompanied by the 
impact of the liquid upon the pipe with such violence as often 
to cause observable or even very heavy shocks ; and often a 
succession of such blows is heard, the intensity of which is the 
greater as the pipe is heavier and larger, and which may be 
startling, and even very dangerous. It is not known precisely 
how this action takes place ; but the Author has suggested 
the following as a possible outline of this succession of phe 
nomena:"^ 

* " Water-hammer in Steam-pipes." Trans. Am. Soc. Mech. Engrs., vol. iv. 
p. 404. 



566 THE STEAM-BOILER. 

The steam, at entrance, passes over or comes in contact 
with the surface of the cold water standing in the pipe. Con- 
densation occurs, at first very slowly, but presently more 
quickly, and then so rapidly that the surface is broken, and 
condensation is completed with such suddenness that a vacuum. 
is produced. The water adjacent to this vacuum is next pro- 
jected violently into the vacuous space, and, filling it, strikes 
on the metal surfaces and with a blow like that of a solid body, 
the liquid being as incompressible as a solid. The intensity of 
the resulting pressure is the greater as the distance through 
which the surface attacked can yield is the less, and enormous 
pressures are thus attained, causing the leakage of joints, and 
even the straining, twisting, and bursting of pipes. In some 
cases the whole of an extensive line or system of pipes has 
'been observed to writhe and jump to such extent as to cause 
well-grounded apprehension. 

The Author once had occasion to test the strength of pipes 
which had been thus already burst. They were 8 inches in 
diameter (20.32 cm.), and of a thickness of f inch (0.95 cm.), and 
had been, when new, subjected to a pressure of about 20 at- 
mospheres (300 lbs. per sq. in.). When tested by the Author 
in their injured condition they bore from one third more to 
nearly four times as high pressures before the cracks which had 
been produced were extended. It is perhaps not absolutely 
certain that some of these pieces of pipe may not have been 
cracked at lower pressures than the above ; but it is hardly 
probable. It seems to the Author very certain that the pres- 
sures attained in his tests were approximately those due to 
the water-hammer, or were lower. The steam-pressure had 
never exceeded about four atmospheres (60 lbs. per sq. in.). 

It is evident that it is not safe, in such cases, to calculate 
simply on a safe strength based on the proposed steam-pres- 
sures ; but the engineer may find those actually met with 
enormously in excess of boiler-pressure, and a '' factor-of-safety" 
of 20 may prove too small, it being found, as above, that the 
water-hammer may produce local pressure approaching, if not 
exceeding, 70 atmospheres (1000 lbs. per sq. in.). These facts. 



STEAM-BOILER EXPLOSIONS. 567 

now well ascertained and admitted, lend some confirmation to 
the Clark and Colburn theory of explosions. 

,277. Energy Stored in Heated Metal is vastly less in 
amount, with the same range of temperature, than in water. 
The specific heat of iron is but about one ninth that of water, 
and the weight of metal liable to become overheated in any 
boiler is usually small. If the whole crown-sheet of a locomo- 
tive-boiler were to be heated to a full red heat, it would only 
store about as much heat per degree as forty pounds (18 kgs.) 
of water, or not far from 30,000 thermal units (7560 calories), or 
23,016,000 foot-pounds (3,030,000 kilog.-m., nearly), or about 
three tenths of the total energy of the fluids concerned in the 
explosion. It would be sufBcient, however, to considerably in- 
crease the quantity of steam present in the steam-space ; and 
this increase, if suddenly produced, and too quickly for the 
prompt action of the safety-valve, might evidently precipitate 
an explosion, which would be measured in its effects by the 
total energy present. 

It thus becomes at once obvious that the danger from the 
presence of this stock of excess energy is determined not only 
by the weight of metal heated and its temperature, but even 
more by the rate at which that surplus heat is communicated 
to the water that may be brought in contact with it, by pump- 
ing in feed-water, or by any cause producing violent ebullition. 
It is probable that this cause has. sometimes operated to pro- 
duce explosions ; but oftener that the loss of strength pro- 
duced by overheating is the more serious source of danger. It 
is also evident that the first is the more dangerous as the pres- 
sures are lower, the second with high pressures. 

As illustrating a calculation in detail, assume \ 7 ^^* ^^/"^^ I 
^ ' I 25 sq. feet \ 

of crown-sheet, or boiler-shell, overheated \ o t- /■ , the 

' ' ( 1000 r.\ 

metal being \ ./<^ , t in thickness, and its total 



^ -s 



weight ] ^^^ Hi' Then the product of weight into 

range of temperature, into specific heat (o.iii), is the measure 
of the heat-energy stored. 



5^8 THE STEAM-BOILER. 

375 X 1000 X O.I 1 1 =41,625 B. T. U., nearly; 
170 X 556 X 0.1 1 1 =10,492 calories, nearly; 

and in mechanical units, 

41,625 X 772 = 32,134,500 foot-pounds nearly; 
10,502 X 423.55 = 4,443,886 kilog.-metres nearly; 

which is fifteen or twenty times the energy stored in the steam 
in a locomotive-boiler in its normal condition, and about one 
half as much as ordinarily exists in water and steam together. 
It is evident that the limit to the destructiveness of explosions 
so caused is the rate of transfer of this energy to the water 
thrown over the hot plate, and the promptness with which the 
steam made can be liberated at the safety-valve. A sudden 
dash of water or spray over the whole of such a surface might 
be expected to even produce a ''fulminating" explosion. For- 
tunately, as experience has shown, so sudden a transfer or so 
complete a development of energy rarely, perhaps never, takes 
place. 

278. The Strength of Heated Metal is known usually to 
decrease gradually with rise in temperature, until, as the weld-' 
ing or the melting-point, as the case may be, is approached, it 
becomes incapable of sustaining loads. Both iron and steel, 
however, lose much of their tenacity at a bright-red heat, at 
which point they have less than one fourth that at ordinary 
temperatures. A steam-boiler in which any part of the furnace 
is left unprotected by the falling of the water-level is very 
likely to yield to the pressure, and an explosion, may result 
from simple weakness. At temperatures well below the red 
heat this will not happen. 

279. ** Low Water," in consequence of the obvious dangers 
which attend it, and the not infrequent narrow escapes which 
have been known, has often been by experienced engineers 
considered to be the most common, even the almost invariable, 
cause of explosions. This view is now refuted by statistics 
and a more extended observation and experience ; but it re- 
mains one of the undeniable sources of danger and causes of 
accident. 

Its origin is usuaUy in some accidental interruption of the 



STEAM-BOILER EXPLOSIONS. 569 

supply of feed-water ; less often an unobserved leak or ac- 
celerated production of steam. Whatever the cause, the 
result is the uncovering of those portions of the heating- 
surface which are highest, and their exposure, unprotected 
by any efficient cooling agency, to the heat of the gases 
passing through the flue at that point. Should it be the 
case of a locomotive or other boiler having the crown-sheet of 
its furnace so placed as to be first exposed when the water- 
level falls, the iron may become heated to a full red heat ; if 
the highest surfaces are those of tubes, through which gases 
approximating the chimney in temperature are passing, the 
heat and the danger are less. In either case danger is incurred 
only when the temperature becomes such as to soften the iron, 
or when the return of the water with considerable rapidity 
gives rise to the production of steam too rapidly to be relieved 
by the safety-valve or other outlet. Such explosions probably 
very seldom actually occur, even when all conditions seem fa- 
vorable. Every boiler-making establishment is continually col- 
lecting illustrations of the fact that a sheet may be overheated, 
and may even alter its form seriously when overheated, without 
completely yielding to pressure ; and the Author has taken 
part in many attempts to experimentally produce explosions 
by pumping feed-water into red-hot boilers, and has but once 
seen a successful experiment. The same operation, in the reg- 
ular workings of boilers, has been often performed by ignorant 
or reckless attendants without other disaster than injury to the 
boiler, but it has unquestionably on other occasions caused 
terrible loss of life and property. The raising of a safety-valve 
on a boiler in which the water is low, by producing a greater 
violence of ebullition in the water on all sides the overheated 
part, may throw a flood of solid water or of spray over it ; and 
it is probable that this has been a cause of many explosions. 
The Author has seen but a single explosion produced in this 
way, although he has often attempted to so produce such a re- 
sult. In three experiments on a plain cylindrical boiler, empty 
and heated to the red heat, the result of rapidly pumping in a 
large quantity of water was in the first the production of a 
vacuum, in the second an excess of pressure safely and easil}^ 



570 THE STEAM-BOILER. 

relieved by the safety-valve, and in the third case a violent ex- 
plosion of the boiler and the complete destruction of the brick 
masonry of its setting.* A committee of the Franklin Institute, 
conducting similar experiments,t had the same experience, 
the pressure " rising from one to twelve atmospheres within 
two minutes" after starting the pump. The most rapid vapor- 
ization occurs, as is well known, at a comparatively low temper- 
ature of metal ; at high temperature the spheroidal condition is 
produced, and no contact exists between metal and liquid. 

Mr. C. A. Davis, President of the New York and Boston 
Steamboat Co., in a letter addressed, Dec. 7, 183 1, to the Col- 
lector of the Port of New York, and answering inquiries of the 
United States Treasury Department, wrote -.% 

" I have noted that by far the greatest number of accidents 
by explosion and collapsing of boilers and flues — I might say 
seven tenths — have occurred either while the boat was at rest, or 
immediately on starting, particularly after temporary stoppages 
to take in or land passengers. These accidents may occur from 
directly opposite causes — either by not letting off e?iougk steaniy 
or by letting off too much: the latter is by far the most de,- 
structive." 

The idea of this writer was that the " letting off of too much " 
steam, producing low-water, was the most frequent cause of 
explosions — an idea which has never since been lost sight of. 

The chief-engineer of the Manchester (G. B.) Steam-boiler 
Association, in 1866-67, repeatedly injected water into over- 
heated steam-boilers, but never succeeded in producing an 
explosion.§ Yet, as has been seen, such explosions may occur. 

A writer in the Journal of the Franklin Institute,! a half- 
century or more ago, asserted that '' the most dreadful accidents 
from explosions which have taken place have occurred from 
low-pressure boilers." It was, as he states, ''a fact that more 
persons had been killed by low than by high pressure boilers." 

* Sci, Am., Sept. 1875. 
\ Jour. Franklin Inst. 1837, vol. xvii. 
X Report on Steam-boilers, H. R., 1832. 
§ Mechanics' Magazine, May, 1867. 
II Vol. iii. pp. 335, 418, 420. 



STEAM-BOILER EXPLOSIONS. 5/1 

Nearly all writers of that time attributed violent explosions to 
low-water, and some likened the phenomenon to that observed 
when the blacksmith strikes with a moist hammer on hot iron. 

Thus, if the boiler is strong, and built of good iron, and not 
too much overheated, or if the feed-water is introduced slowly 
enough, it is possible that it may not be exploded ; but with 
weaker iron, a higher temperature, or a more rapid development 
of steam, explosion may occur. Or, if the metal be seriously 
weakened by the heat, the boiler may give way at the ordinary 
or a lower pressure ; which result may also be precipitated by the 
strains due to irregular changes of dimensions accompanying 
rapid and great changes of temperature. 

Explosions due to low-water, when there is a considerable 
mass of w^ater below the level of the overheated metal, are some- 
times fearfully violent ; a boiler completely emptied of w^ater, 
and only exploded by the volume of steam contained wdthin it, 
is far less dangerous. Low-water and red-hot metal in a loco- 
motive or other firebox boiler are for this reason far more dan- 
gerous than in a plain cylindrical boiler, since, as was indicated 
by the experiments conducted by the Author, the latter must be 
entirely deprived of w^ater before this dangerous condition can 
arise. In the course of the numerous experiments already al- 
luded to, many attempts wxre made to overheat the latter class 
of boiler; but none were successful until the water was entirely 
expelled. Experiments with apparatus devised for the purpose 
of keeping the steam moist under all circumstances indicate 
that it is difficult if not impossible to overheat even an un- 
covered firebox crown-sheet if the steam be kept moist, and 
that such steam is very nearly as good a cooling medium, in 
such cases, as the w^ater itself. 

Fig. 125"^ represents a boiler exploded by the introduction 
of water after it had been emptied by carelessly leaving open 
the blow-cock. This boiler w^as about five years old ; and the 
explosion, as is usual in such cases, was not violent, the small 
amount of water entering and the w^eakness of the sheet con- 
spiring to prevent the production of very high pressure or the 

* The Locoj/iotive, Sept. i8S6, p. I2g. 



572 



THE STEAM-BOILER. 



storage of much energy. The whole of the lower part of the 
shell of the boiler was found, on subsequent examination, to 
have been greatly overheated. One man was killed by the fall- 
ing of the setting upon him ; no other damage was done. 




Fig. 125.— Boiler Exploded. Cause, Low-water. 



Fig. 126 shows the effect of a similar operation on a water- 
tube boiler. The feed-water was cut off, and not noticed until 

the water-level became so low that 
the boiler was nearly empty and 
the tubes were overheated. One 
of the tubes burst, and the damage 
cost of $15, and the works were 



Fig. 126.— Tube Burst; Low-water. 



was speedily repaired at a 
running the next day."^ 

That low-water and the consequent overheating of the 
boiler does not necessarily produce disaster, ev«n when the 
water is again supplied before cooling off, was shown as early 
as 181 1, by the experience of Captain E. S. Bunker of the 
Messrs. Stevens' steamboat Hope, then plying between New 
York and Albany. During one of the regular passages he dis- 
covered that the water had been allowed by an intoxicated fire- 
man to completely leave both the boilers. He at once started 
the pump, and, filling up the boilers, proceeded on his way, no 
other sign of danger presenting itself than *' a crackling in the 



* G. H. Babcock. 



STEAM-BOILER EXPLOSIONS. 573 

boiler as the water met the hot iron, the sound of which was 
like that often heard in a blacksmith's shop when water is 
thrown on a piece of hot iron." "^ A year later Captain Bunker 
repeated this experience at Philadelphia on the Phoenix, 
where the boilers were of the same number and size as those 
of the Hope.f 

Defective circulation may cause the formation of a volume 
of steam in contact with a submerged portion of the heating- 
surface. The Author, when in charge of naval boilers during 
the civil war, 1 861-5, found it possible on frequent occasions 
to draw a considerable volume of practically dry steam from the 
water-space between the upper parts of two adjacent furnaces 
at a point two or three feet below the surface-water level. 
After drawing off steam for a few seconds, through a 
cock provided to supply hot water for the engine and fire- 
rooms, water would follow as in the normal condition of the 
boiler. This condition often occurs in some forms of boiler, 
and has been occasionally observed by every experienced en- 
gineer. It would not seem impossible, therefore, that steam 
might be sometimes thus encaged in contact with the furnace, 
and thus cause overheating of the adjacent metal. Many such 
instances have been related ; but they have been commonly 
regarded by the inexperienced as somewhat apocryphal. :J: 

In order that the danger of overheating the crown-sheet of 
the locomotive type of boiler may be lessened, it is very usual 
to set it lower at the firebox end, when employed as a station- 
ary boiler, so as to give a greater depth of water over the 
crown-sheet than over the tubes at the rear. The plan of giv- 
ing greatest depth of water, when possible, at that end of the 
boiler at which the heating-surfaces near the water-surface are 
hottest is always a good one. 

Mr. Fletcher concluded from his experiments that low-water 
is only a cause of danger by weaking the overheated plates. He 
says:§ 

*Doc. No. 21, H. R. , 25th Congress, 3d Session, 1838, p. 103. 

t Ibid. 

X See London Engineer, Dec. 7, i860, pp. 371, 403. 

§ London Engineer, Mar. 15, 1867, p. 228. 



574 THE STEAM-BOILER. 

"■ These experiments, it is thought, may be accepted as 
conclusive that the idea of an explosion arising from the in- 
stantaneous generation of a large amount of steam through the 
injection of water on hot plates is a fallacy." 

The conclusion of the Author, in view of the experiments of 
the committee of the Franklin Institute and of his own per- 
sonal experience in the actual production of explosions by 
this very process, as elsewhere described, does not accord with 
the above ; but it is sufificiently well established that low-water 
may frequently occur and feed-water may be thrown upon the 
overheated plates without necessarily causing explosion. Dan- 
ger does, however, unquestionably arise, and such explosions 
have most certainly occurred — possibly many in the aggre- 
gate. 

Low-water is certainly very rarely, perhaps almost never, 
the cause of explosion of other than firebox boilers ; in these, 
however, the danger of overheating the crown-sheet of the 
furnace, if the supply of water fails, is very great, and in such 
cases explosion is always to be feared. The most disastrous 
explosions are usually those, however, in which the supply of 
water is most ample. 

280. Sediment and Incrustation sometimes produce the 
effect of low-water in boilers, even where the surfaces affected 
are far below the surface of the water. Every increase of re- 
sistance to the passage of heat through the metal and the in- 
crusting layer of sediment or scale causes an increase of tem- 
perature in the metal adjacent to the flame or hot gases, until, 
finally, the incrustation attaining a certain thickness, the iron 
or steel of the boiler becomes very nearly as hot as the gases 
heating it. Should this action continue until a red heat, or a 
white heat even, as sometimes actually occurs, is reached, the 
resistance becomes so greatly reduced that the sheet yields, 
and either assumes the form of a ''pocket" or depression, as 
often happens with good iron or with steel, or it cracks, or it 
even opens sufficiently to cause an explosion. " Pockets" 
often form gradually, increasing in extent and depth day by 
day, until they are discovered, cut out, and a patch or a new 
sheet put in, or until rupture takes place. In such cases the 



S TEA M-B OILER EXPL SIONS. 



575 



incrustation keeps the place covered while permitting just 
water enough to pass in to cause the extension of the defect. 

In some cases the process is a different and a more disas- 
trous one : The scale covers an extended area, permitting it 
to attain a high temperature. After a time a crack is pro- 
duced in the scale by the unequal expansion of the two sub- 
stances and the inextensibility of the incrustation ; and water 
entering through this crack is exploded into steam, ripping off 
a wide area of incrustation previously covering the overheated 
sheet, and giving rise instantly, probably, to an explosion 
which drives the sheet down into the fire, and may also rend 
the boiler into pieces, destroying life and property on every 
side. Such an explosion usually takes place with the boiler 
full of water and its stored energy a maximum, and the result 
is correspondingly disastrous. 

Certain greasy incrustations and some floury forms of min- 
eral or vegetable deposits have been found peculiarly danger- 
ous, as, in even exceedingly thin layers, they are such perfect 
non-conductors as to speedily cause overheating, strains, cracks, 
leakage, and often explosion. M. Arago mentions a case in 
which rupture occurred in consequence of the presence of a rag 
lying on the bottom of a boiler. ^^ 

The effect of incrustation in causing the overheating of the 
fire-surfaces, the formation of a " pocket " and final rupture, is 
well shown in the illustrations which- follow. 

When the water is fully up to the safe level, as at the right 
in the first of the two figures, the heat received from the fur- 
nace-gases is promptly -carried 
away by the water, and the sheet 
is kept cool. When the water 
falls below that level, or is pre- 
vented by incrustation from 
touching the metal, as in the left- 
hand illustration, the sheet be- 
comes red-hot, soft, and weak, Fig. 127.— Overheating the Sheet. 

and yields as shown. When this goes on to a sufficient extent, 





* Report of the Committee of the Franklin Institute. 



5/6 



THE STEAM-BOILER. 



as on a horizontal surface (Fig. 128), a pocket is produced. The 
illustration represents a sheet removed from the shell of an ex- 
ternally fired boiler thus injured. 




Fig. 128.— a " Pocket. 



Finally, when the defect is not observed and the injured 
sheet removed, the metal may finally give way entirely, per- 




FiG. 129. — Ruptured Pocket. 



mitting the steam and water to issue, as in the last illustration 
of the series, in which this last step in the process is well 
represented. Where the area thus affected is considerable. 




Fig. 130.— Shell Ruptured. 



the result may be a general breaking up of that portion of the 
shell, as in the next figure, and an explosion may prove to be 
the final step in the chain of phenomena described. In other 
cases, where, as in the next sketch, a Hne of weakness may be 



STEAM-BOILER EXPLOSIONS. 



S77 



the result of other causes, a large section of the boiler may 
be broken out, as at AD, Fig. 131. 




Extended Rupture. 




Fig. 132. — Incrustation in 
Feed-pipe. 



The deposition of sediment and of scale takes place not 
only in the boiler, but also with some kinds of water, in 
the feed-pipe, as is illustrated in the 
accompanying engraving, which is 
made from an actual case in which 
the pipe was so nearly filled as to 
become quite incapable of perform- 
ing its office. A current has appar- 
ently no effect, in many such cases, 
in preventing the deposition of scale. 
The Author has known hard scale to form in the cones of a 
Giffard injector under his charge, where the stream was mov- 
ing with enormous velocity, and loudly whistlmg as it passed. 

Instances are well known of the explosion, with fatal effect, 
of open vessels, in consequence of the action above described. 
Mr. G. Gurney in 1831 gave an account of such an explosion 
of the water in an open caldron, at Meux's brewery, by which 
one person was killed and several others injured.^ It was found 
that the bottom had become incrusted with sediment, and the 
sudden rupture of the film, permitting contact of the water 
above with the overheated metal below, caused such a sudden 
and violent production of steam that it actually ruptured the 
vessel. The process of which this is an illustration is precisely 
analogous to suddenly throwing feed-water into an overheated 
boiler. 



* Report on Steam Carriages. Doc. loi, 22d Congress, ist Session, p. 31. 
37 



S/S THE STEAM-BOILER. 

281. Energy stored in Superheated Water has been 
sometimes considered a source of danger to steam-boilers and 
a probable cause of explosions. The magnitude of this stock 
of energy is not likely to differ greatly from that of water at 
the same temperature under the pressure due that tempera- 
ture, and for present purposes specific heat may be taken as 
unity. The quantity of heat so stored is therefore measured 
very nearly by the product of the weight of water so overheated, 
the mean range of superheating, and the specific heat here 
taken as unity. It is not known how large a part of the water 
in any boiler can be superheated, or the extent to which this 
action can occur. It is often doubted, however, whether it can 
take place at all in steam-boilers. 

This condition occurring, the experiments of MM. Donny, 
Dufour, and others show that the larger the mass of Avater 
the less the degree of superheating attainable ; the more im- 
pure the water, or the greater the departure from the condi- 
tion of distilled water, and the larger the proportion of air or 
sediment mechanically suspended, the more difficult is it to at- 
tain any considerable superheating. 

As early as 1812,^ Gay-Lussac observed a retardation of 
ebulhtion in glass vessels; thirty years later,f M. Marcet found 
that water deprived of air can be raised several degrees above 
its normal boiling-point; while Donny,:}: Dufour,§ Magnus, || 
and Grovelf all succeeded in developing this phenomenon more 
or less remarkably. Donny, sealing up water deprived of air 
in glass tubes, succeeded in raising the boiling point to 138° C. 
(280° F.j, at which temperature vaporization finally occurred 
explosively. Dufour, by floating globules of pure water in a 
mixture of oils of density equal to that of the water, succeeded 
with very minute globules in raising the boiling-point to 175° 
C. (347° F.), at which temperature the normal tension of its 

* Ann. de Chimie et de Physique, Ixxxii. 
f Bibl, Univ. xxxviii. 

X Ann. de Ch. et de Phys., 3me serie, xvi. 
§ Bibl. Univ., Nov, 1861, i. xii. 
I| Poggendorff's Ann. t. cxiv. 
1[ Cosmos. '863. 



STEAM-BOILER EXPLOSIONS. S79 

steam is 115 pounds per square inch (nearly eight atmospheres) 
by gauge. In such cases the touch of any soHd or of bubbles 
of gas would produce explosive evaporation. Solutions always 
boil at temperatures somewhat exceeding the boiling-point of 
water, but usually quietly and steadily. In all these cases the 
rise in temperature seems to have been the greater the smaller 
the mass of water experimented with. 

In all ordinary cases of steam-boiler operation the mass of 
water is simply enormous as compared with the quantities em- 
ployed in the above-described laboratory experiments ; the 
water is almost never pure, and probably as invariably contains 
more or less air. It would seem very unlikely that such super- 
heating could ever occur in practice. There is, however, some 
-evidence indicating that it may. 

Mr. Wm. Radley'^ reports experimenting with small labora- 
tory boilers of the plain cylindrical form, and continuing slowly 
heating them many hours, finally attaining temperatures ex- 
ceeding the normal by 15^ F. (8°. 3 C). The investigator con- 
cludes : 

''Here we have conclusive data suggesting certain rules to 
be vigorously adopted by all connected with steam-boilers who 
would avoid mysterious explosions : First, never feed one or 
more boilers with surplus water that has been boiled a long 
time in another boiler, but feed each separately. Second, when 
boilers working singly or fed singly are accustomed, under high 
pressure, to be worked for a number of hours consecutively, 
day and night, they should be completely emptied of water at 
least once every week, and filled with fresh water. Third, in 
the winter season the feed-water of the boiler should be sup- 
plied from a running stream or well ; thaw water should never 
be used as feed for a boiler." 

'' Locomotive, steamboat, and stationary engine boilers have 
their fires frequently banked up for hours, without feeding water, 
and the steam fluttering at the safety-valve, so as to have them 
all ready for starting at a moment. This is a dangerous prac 
tice, as the foregoing experiments demonstrate. While so 

* London Mining /ournal, June 28, 1856. 



58o THE STEAM-BOILER. 

standing, all the atmospheric air may be expelled from the 
water, and it may thereby attain to a high heat, ready to gen- 
erate suddenly a great steam-pressure when the feed-pump is 
set in motion. This is, no doubt, the cause of the explosion 
of many steam-boilers immediately upon starting the engine, 
even when the gauge indicates plenty of water. The remedy 
for such explosions must be evident to every engineer — keep 
the feed-pump going, however small may be the feed re- 
quired." 

On the other hand, the report of a committee appointed by 
the French Academy to inquire into the superheated-water 
theory of steam-boiler explosions indicates at least the difficulty 
of securing such conditions.* The committee constructed suit- 
able apparatus, experimented in the most exhaustive manner, 
and investigated several explosions claimed by the advocates of 
the theory to have been due to this cause. They failed to su- 
perheat water under any conditions which could probably occur 
in practice, and the explosions investigated were shown conclu- 
sively to have resulted from simple deterioration of the boilers, 
or from carelessness. It is unquestionably the fact that explo- 
sions due to this cause are at least exceedingly rare, although 
it is not at all certain that they may not now and then take 
place. The ocean is constantly being traversed by thousands 
of steamers having surface-condensers and boilers in which the 
water is used over and over again, and in which every condition 
is seemingly favorable to such superheating of the water ; but 
no one known instance has yet occurred of the production of 
this phenomenon, there or elsewhere, on a large scale, where 
boilers are in regular operation. 

M. Donny, who first suggested the possibility of this action 
as a cause of boiler-explosions, has had many followers. M. 
Dufour,f who doubts if such explosions are possible in the or- 
dinary working of the boiler, points out the fact, however, that 
boilers which are not in operation, but which are quietly cool- 
ing down after the working-hours are over, are peculiarly well 

* Annales de Mines, 1886. 

f Sur TEbullition de I'Eau, et sur una cause probable d' Explosion des Chau- 
dieres a Vapeur, p. 29. 



STEAM-BOILER EXPLOSIONS. 58 1 

situated for the development of this form of stored energy. He 
points out the known fact that many explosions have taken 
place under such conditions, the pressure having fallen below 
the working-pressure. M. Gaudry* makes the same observa- 
tion. Such cases are supposed to be instances of " retarded 
ebullition" with decrease of pressure and superheating of the 
water. Many circumstances unquestionably tend to strengthen 
this view. 

So tremendous are the effects of many explosions that M. 
Audrand has expressed the belief that a true explosion must be 
preceded by pressures approaching or exceeding 200 atmos- 
pheres ;t an intensity of pressure, however, which no boiler 
could approximate. Mr. Hall also thinks that the shattering 
effect sometimes witnessed, resulting in the shattering of a 
boiler into small pieces, must be the effect of a sudden and 
•enormous force, partaking of the nature of a blow \X and cites 
cases, such as are now known to be common, of an explosion 
taking place on starting an engine, after the boiler has been at 
rest and making no steam for a considerable time. M. Arago 
cites a number of similar instances,§ and Robinson a number 
in still greater detail. || Boilers after quietly '' simmering" all 
night exploded at the opening of the throttle-valve or the 
safety-valve in the morning. The locomotive Wauregan, 
Avhich exploded Avithin sight and hearing of the Author at Prov- 
idence, R. I., in February, 1856, is mentioned by Colburn as 
such a case. The engine had been quietly standing in the en- 
gine-house two hours, the engineer and fireman engaged clean- 
ing and packing, preparatory to starting out. The explosion 
was without warning and very violent, stripping off the shell 
and throw^ing it up through the roof, and killing the engineer, 
who was standing beside his engine. 

Mr. Robinson^ thinks the usual cause of such explosions is 

* Traite des Machines a Vapeur. 
f Coniptes Rendus, May, 1855, p. 1062. 

X Civil Engitieers' Journal, 1856, p. 133 ; Dingler's Journal, 1856, p. 12. 
§ Annuaire, 1830. 
11 Steam-boiler Explosions, p. 62. 
1 Ibid. p. 66. 



582 THE STEAM-BOILER. 

the overheating of the water, the phenomenon being in its ef- 
fects very like the "water-hammer" in steam-pipes, producing 
shocks which the Author has shown to give rise to instantaneous 
pressures exceeding the working pressures ten or twenty times ; 
the action seems, however, rather to be that ''boiUng with 
bumping" famihar to chemists handHng sulphuric acid in con- 
siderable quantities. Instances have been known in which this 
bumping has burst pipes or severely shaken boilers and setting 
without producing explosion. 

The deaeration of water, and the consequent superheat- 
ing of the liquid, to which some explosions have been attrib- 
uted, are phenomena which have been often investigated. Mr. 
A. Guthrie, formerly U. S. Supervising Inspector-General of 
Steam-vessels, states that he has made many such experiments,, 
as follows :* 

''(i) In my experiments I first procured a sample of water 
from the boiler of an ordinary condensing-engine ; here, of 
course, in addition to being subjected to long-continued boil- 
ing, it had passed through the vacuum. 

" (2) I procured a sample from the ordinary high-pressure 
non-condensing engine-boiler, which before entering the boiler 
had passed the heater at 210°. 

" (3) I procured some clean snow and dissolved it under oil^ 
so that there was no contact with the air. 

'■' (4) I froze some water in a long, upright tube, using only 
the lower end of the ice when removed from the tube, and dis- 
solved under oil. 

"(5) I placed a bottle of water under a powerful vacuum- 
pump worked by steam, for two hours ; agitating the water 
from time to time to displace any air that might possibly be 
confined in it, then closed it by a stop-cock, so that no air 
could possibly return. 

'' (6) I boiled water in an open boiler for several hours, and 
filled a bottle half-full, closed and sealed it up, so that when it 
became cool it would in effect be under a vacuum, agitating it 
as often as seemed necessary. 

^American Artisan; Locomotive, i88o. 



STEAM-BOILER EXPLOSIONS. 5^3 

" (7) Another bottle was filled with the same, and sealed. 

" (8) I next took some clean, solid ice, dissolved it under 
oil,, and brought it to a boil, which was continued for an hour or 
more, after which it was tightly corked. 

" (9) I procured a bottle of carefully-distilled water, after 
long boiling and having been perfectly excluded from air during 
the distillation. 

"(10) I obtained a large number of small fish, placed them 
in pure, clean water in an open-headed cask, on a moderately 
cold night, so that very soon it became frozen over, conse- 
quently excluding the air, the fish' breathing up the air in the 
water, so that (if I am correct in this theory) a water freed from 
air would be the result ; but in some of these different processes, 
if not in all, I was likely to free the water from air, if it could 
ever possibly occur in the ordinary course of operating a steam- 
boiler. 

*' Having procured a good supply of glass-boilers adapted to 
my purpose, and so made that the slightest changes could be 
noted, and using as delicate thermometers as I could obtain, I 
took these samples, one after another, and brought them to the 
boiling-point ; and every one, with no variation whatever, boiled 
effectually and positively at 212° Fahrenheit or under ; nor was 
there the slightest appearance of explosion to be observed." 

This evidence is, of course, purely negative. 

The superheating of water, on- even the small scale of the 
laboratory experiments of Donny, Dufour, and others, has never 
been successfully performed, except with the most elaborate 
precautions. The vessel containing the liquid must be abso- 
lutely clean ; the washing of all surfaces with an alkaline solu- 
tion seems to be one of the customary preliminary operations. 
The vessel must usually be heated in a bath of absolutely uni- 
form temperature in order that currents may not be set up 
within the body of the liquid to be heated ; no solid can be per- 
mitted to enter or come in contact with it; no shock can be al- 
lowed to affect it ; even contact with a bubble of gas may stop 
the process of superheating. All these conditions are as far re- 
moved as possible from those existing in steam-boilers. 

282. The Spheroidal State, or Leidenfrost's phenomenon. 



584 THE Steam-boiler. 

as it is often called, is a condition of the water, as to tempera- 
ture, precisely the opposite of that last described, its tempera- 
ture being less, rather than greater, than that due the pressure ; 
while the adjacent metal is always greatly overheated, and thus 
becomes a reservoir of surplus heat-energy which can be trans- 
ferred at any instant to the water. This peculiar phenomenon 
was first noted by M. Leidenfrost about 1746. It was studied 
by Klaproth, Rumford, and Baudrimont,* and more thoroughly 
by Boutigny. 

When a small mass of liquid rests upon a surface of metal 
kept at a temperature greatly exceeding the boiling-point of 
the liquid under the existing pressure, the fluid takes the form 
of a globule if a very small mass, or of a flattened spheroid or 
round-edged disk if of considerable volume, and floats around 
above the metal, quite out of contact with the latter, and grad- 
ually, very slowly, evaporates. The higher the temperature of 
the plate, the more perfect this repulsion of the liquid. Should 
the temperature of the metal fall, on the other hand, the globule 
gradually sinks into contact \w\\\\ it, and, at a temperature which 
is definite for every liquid, and is the lower as it is the more- 
volatile, finally suddenly absorbs heat with great rapidity and 
evaporates often almost explosively. If contact is forcibly pro- 
duced at the higher temperature of the supporting plate of 
metal, as under a blacksmith's hammer, a real explosion takes 
place, throwing drops of the liquid in every direction. 

M. Boutigny found the temperature of contact to be, for 
water, alcohol, and ether, respectively, 142° C, 134°, and 61° 
(287° F., 273°, and 142°). In all cases the temperature of the 
liquid was independent of that of the metal, and somewhat be- 
low the boiling-point. It is found, also, that a real and power- 
ful repulsion is produced between metal and liquid ; this is sup- 
posed to be due, in part at least, to the cushion of vapor there 
interposing itself. Contact is accelerated by the introduction 
of soluble salts into the liquid. 

It is supposed by many writers that this phenomenon may 
play its part in the production of explosions of steam-boilers, 

■^ Ann. de Chemie et de Physique, 2d series, t. Ixi. 



STEAM-BOILER EXPLOSIONS. 5^5 

and especially in cases in which there seems some evidence that, 
immediately before the explosion, there was no apparent over- 
heating of the parts exposed to the action of the fire, and in 
those still more remarkable instances in which the shattered 
parts had been, to all appearance, much stronger than other por- 
tions which had not been ruptured ; no evidence existing of low- 
water or overheating at the furnace, and the pressure being, the 
instant before the accident, at or below its usual working figure. 
Bourne^ has no doubt that this does sometimes take place. 
Colburn gives a number of instances of explosions taking place 
under, apparently, precisely such conditions; and Robinsonf 
also cites several, in some of which the plates of the shell were 
badly shattered, as by a concussive force. In some such in- 
stances evidences of overheating, but only far below the water- 
level, known to have existed immediately before the explosion, 
have been observed, indicating repulsion to have there occurred. 
This latter is simply still another instance of bringing about the 
same results as when pumping water into an overheated boiler 
in which the water is low. 

Mr. Robinson:}: tells of a case in which a nearly new locomo- 
tive, standing in the house, with a pressure, as shown but a 
moment before by the steam-gauge, of but 40 pounds, — one 
third its presumed safe v/orking pressure, — the fire low and every- 
thing perfectly quiet, exploded with terrible violence, shatter- 
ing the top of the boiler directly over the firebox into many 
parts. That such explosions might occur were the metal actu- 
ally overheated under water, is shown by experiences not at all 
uncommon. 

In the work of determining the temperatures of casting al- 
loys tested by the Author § for the United States Board ap- 
pointed in 1875 to test iron, steel, and other metals, at the first 
casting of a bar composed of 94.10 copper, 5.43 tin, while pouring 
the metal into the water for the test, an explosion took place 
which broke the wooden vessel which held the water, and threw 

* Treatise on the Steam-engine. 1868. 

f Steam-boiler Explosions, p. 33. 

X Steam-boiler Explosions, p. 62. 

§ Report on Copper-tin Alloys. Washington, 1879. 



586 



THE STEAM-BOILER. 



water and metal about with great violence. It appears probable 
that the metal was heated to an unusually high temperature, as 
in pouring other metals when at a dazzling white heat explo- 
sions sometimes took place, but they were usually not violent 
enough to do more than make a slight report as the hot metal 
touched the water. Another bar was cast at an extremely high 
temperature, being at a dazzling white heat. On pouring a 
small portion into water in attempting to obtain the temperature, 
a severe explosion took place, and this was repeated every time 
that even a small drop of the molten metal touched the water. 
The cold ingot-mould was then filled with this very hot metal. 
After the metal remaining in the crucible had stood for several 
minutes and had cooled considerably, it could be poured into 
water without causing the slightest explosion. Thus it would 
seem that the temperature at which contact with the water is 
produced may have an important effect upon the violence with 
which the steam is generated, and that of the explosion so pro- 
duced. The explosions sometimes taking place with fatal effect 
in foundries when molten metal is poured into damp or wet 
moulds are produced in the manner above illustrated. They 
are usually apparently of the " fulminating class." Another in- 
stance occurred within the cognizance of the Author, even more 
striking than either of the above.* 

Two workmen in a gold and silver refinery were engaged in 
"graining" metal, which process consists in pouring a small 
stream of melted metal into a barrel of water, while a stream of 
water is also run into the barrel to agitate the water already 
there. Suddenly an explosion occurred which literally shivered 
the barrel, and threw the workmen across the room. Every 
hoop of the barrel, stout hickory hoops, was broken. The 
staves, seven eighths of an inch thick, and of oak, were not only 
splintered, but broken across ; and the bottom, which was resting 
on a flat surface, and which was of solid oak an inch in. thick- 
ness, was split and broken across the grain. A box on which 
stood the man who was pouring the metal was converted into 
kindling wood. The metal, though scattered somewhat, for the 



* Reported in the Providence (R. I.) Jottrnal, Feb. 2, 1881. 



STEAM-BOILER EXPLOSIONS. 587 

most part remained in place, but the water was thrown in all 
directions. 

This explosion of an open barrel, like the preceding cases, 
was evidently due to the deferred thermal reaction of the water 
with a mass of very highly heated metal, with which it was 
finally permitted to come in contact at a temperature which 
allowed an explosive formation of steam. This class of explo- 
sions, by which open vessels are shattered and the water con- 
tained in them atomized, are by many engineers believed to 
exemplify the terrible explosions fulminantes of French writers 
on this subject. 

The temperature of maximum vaporization, with iron plates, 
was reported by the committee of the Franklin Institute to be 
346^° F. (175° C.) and that of repulsion 385° F. (196° C), and 
to be the same under all pressures. Any cause which may retard 
the passage of heat from the iron to the water, though but the 
thinnest film of sediment, grease, or scale, may permit such in- 
crease of temperature as may lead to repulsion of the water, the 
overheating of the metal, the production of the spheroidal condi- 
tion, and the accidents due to that phenomenon, provided that 
the fire be so driven as to supply more heat than can be dis- 
posed of in ordinary working by the circulation and vapori- 
zation then going on. Robinson's experiments with safety- 
plugs indicate that a good circulation is usually a sufficient 
insurance against this action ; and experience with the boilers 
of locomotives and of torpedo-boats, in which from 50 to 100 
pounds of coal per square foot {2AA to 488 kilogs. on the square 
metre) of grate are burned every hour, shows that the risk, with 
steam-boilers of good design, is not great. With impure water 
and defective circulation Robinson observed many instances of 
singular and dangerous phases of this action."^ It is suggested 
that many explosions of locomotives on the road or at stations 
may be due to the impact, on the shells of their boilers, of 
water thus projected from overheated iron below the water-line. 
In many such cases the engines have not left the rails, the 
break taking place just back of the smoke-box or near the fire- 

* See his Steam-boiler Explosions, pp. 40-46. 



588 THE STEAM-BOILER. 

box, and from the impact of water thus thrown from the tube- 
sheets. 

M. Melsen"^ experimentally proved it possible to prevent 
the occurrence of the spheroidal condition by the distribution 
of spurs or points of iron over the endangered sheets. 

The conductivity of the metal has an important influence on 
the effect of contact, suddenly produced, between the red-hot 
solid and the liquid. Professor Walter R. Johnson observed, in 
his elaborate experiments,f that brass produced much greater 
agitation of the water when submerged at the red heat than did 
iron. He also noted the singular fact that water at the boiling- 
point, thrown upon red-hot iron, requires more time for evapo- 
ration than cold water, probably in consequence of the greater 
efficacy of the latter in bringing down the temperature of the 
metal to that of maximum rapidity of action. The contact 
with the iron of incrustation, oxide, or other foreign matter ac- 
celerated this process also. Johnson found that beyond the 
temperature of maximum repulsion vaporization was acceler- 
ated by further elevation of temperature. 

At the meeting of the British Association in 1872, Mr. B,ar- 
rett read a paper upon the conditions affecting the spheroidal 
state of liquids and their possible relationship to steam-boiler 
explosions. The presence of alkalies or soaps in water percep- 
tibly aids in the production of the spheroidal state. A copper 
ball immersed in pure water produced a loud hissing sound and 
gave off a copious discharge of steam. On adding a little soap 
to the water the ball entered the liquid quietly. Albumen, 
glycerine, and organic substances generally produced the same 
result. The best method is to use a soap solution, and to plunge 
into this a white-hot copper ball of about two pounds weight. 
The ball enters the liquid quietly, and glows white hot at a 
depth of a foot or more beneath the surface. Even against 
such pressure the ball will be surrounded with a shell of vapor 
of an inch in thickness. The reflection of the light from the 
bounding surfaces of the vapor-bubble surrounding the glowing 



* Bull, de rAcademie Royale de Belgium, April, 1871. 
f Reports on Steam-boilers, H. R., 1832, p. iii. 



W 



STEAM-BOILER EXPLOSIONS. 589 

ball gives to the envelope the appearance of burnished silver. 
As the ball gradually cools, the bounding envelope becomes 
thinner, and finally collapses with a loud report and the evolu- 
tion of large volumes of steam. Mr. Barrett makes the sugges- 
tion that the traces of oil, or other organic matters which find 
their way into a steam-boiler, may similarly produce a sudden 
generation of steam sufficient to account for certain problemati- 
cal explosions, and thus lends some strong confirmatory evidence 
to the idea often promulgated by others within and without the 
engineering profession. 

283. Steady Rise in Pressure has been shown by the 
experiments of the committee of the Franklin Institute, and 
by numerous cases of explosion, both before and since their 
time, to be capable of producing very violent explosions. In 
such cases, the steam being formed more rapidly than it is 
given exit, the pressure steadily increases until a hmit is found 
in the final rupture of the weakest part of the boiler. Should 
this break occur below the water-line, and be the result of long 
decay or injury, no explosion may ensue ; but should the rup- 
ture be extensive, or should it occur above or near the surface 
of the water, the succession of phenomena described by Clarke 
and Colburn may follow, and an explosion of greater or less 
violence may take place. The intensity of the effect will de- 
pend largely upon the quantity of stored energy liberated, and 
partly upon the suddenness with which it is set free. A slowly- 
ripping seam or gradually extending crack would permit a 
far less serious effect than the general shattering of the shell, 
or an instantaneously produced and extensive rent. 

The time required to produce a dangerous pressure is easily 
calculated when the weight of water present, W, the range of 
temperature above the working pressure and temperature, 
/j — t^, and the quantity of heat, Q, supplied from the furnace 
are known, and is 

w{t: -t : 

Q '- 

Professor Trowbridge gives the following as fair illustrations 
of suc-h cases :* 

* Heat as a Source of Power, p. igi. 



590 THE STEAM-BOILER. 

(i) A marine tubular boiler is of the largest size, such that 
W ~ 79,000 lbs. of water. 

Suppose the working pressure to be 2\ and the dangerous 
pressure 4 atmospheres. 

The boiler contains 5000 square feet of heating-surface ; 
and supposing the evaporation to be 3 lbs. of water per hour 
for each square foot, we shall have, taking 1000 units of heat 
as the thermal equivalent of the evaporation of i lb. of water, 

t,- t^ 29° F. 

5000 X 3 X 1000 



_ 70,000 X 2Q 

= 9.1 mmutes. 



5000 X 3 X 1000 
65 

(2) A locomotive boiler, containing 5000 lbs. of water, hav- 
ing 1 1 square feet of grate-surface, and burning 60 lbs. of coal 
per hour on each square foot of grate, each pound of coal 
evaporates about 7 lbs. of water per hour, making J J lbs. of 
water evaporated per minute. 

Suppose the working pressure to be 90 lbs., and the danger- 
ous pressure to be 175, 

t,-t= 50° F. 

5000 X 50 , . ^ 

T— = 3i mmutes. 

JJ — 1000 ^^ 

(3) The Steam Fire-engine. — The boiler contains 338 lbs. 
of water and 157 square feet of heating-surface. Supposing 
each square foot of heating-surface to generate but i lb. of 
steam in one hour, the pressure will rise from 100 to 200 lbs. in 

7" r= 7 minutes. 

(4) To find, in the same boiler, how long a time will be re- 
quired to get up steam; that is, to carry the pressure to 100 lbs. 



STEAM-BOILER EXPLOSIONS. 59 1 

If we suppose but i^ cubic feet of water in the boiler, we shall 
have 

^ 93 X 117 . , 

7^ — « — s««_«^— = 4. 1 minutes. 
157X 1000 



60 

Thus, if ^is diminished, the time T is diminished in the 
same proportion. The lowering of the water-level from failure 
of the feed-apparatus increases the danger, not only by expos- 
ing plates to overheating, but by causing a more rapid rise 01 
pressure for a given rate of combustion. 

Gradual increase of pressure can never take place if the 
safety-valve is in good order, and if it have sufficient area. 

The sticking of the safety-valve, either of its stem or its 
seat, the bending of the stem or the jamming of the valve by 
a superincumbent object or lateral strains, and similar accidents, 
have produced, where boilers were strong and otherwise in 
good order, some of the most terrific explosions of which we 
have record. The parts of the boiler have been thrown enor- 
mous distances, and surrounding buildings and other objects 
levelled to the ground, while the report has been heard miles 
away from the scene of the disaster. 

The records of the Hartford company up to 1887 include 
accounts of 26 explosions of vessels detached from the generat- 
ing boiler, used at moderate pressures for various purposes in 
the arts, and there have been many others of less importance 
that were not considered worthy of public mention. It is con- 
cluded that the percentage of explosions among bleaching, 
digesting, rendering, and other similar apparatus is ten times 
greater than among steam-boilers at like average pressures, and 
the destructive work done is quite as astonishing as that by the 
explosion of ordinary steam-generators,^ 

This is sufficiently decisive of the question whether it is 
possible to produce destructive explosions of boilers simply by 
excess of pressure above that which the vessel is strong enough 
to withstand. In these cases low-water and all the other 
special causes operating where fire and high temperatures exist, 

* The Loco?notive, 1887. 



592 THE STEAM-BOILER. 

and such absurd theories as the generation of gas or the actiort 
of electricity, are ehminated ; and it is seen that mere deteri- 
oration and loss of strength, or a rise of steam-pressure, even 
where there is an ample supply of water, may produce explo- 
sions of the utmost violence. 

284. The Relative Safety of Boilers of the various types 
is determined mainly by their general design, and their greater 
or less liability to serious and extensive injury by the various 
accidents and methods of deterioration to which ail are to a 
greater or less extent liable. The two essential principles by 
which to compare and to judge the safety of boilers are : 

(i) Steam-boilers should be so designed, constructed, oper- 
ated, inspected, and preserved as not to be liable to explosion. 

(2) Boilers should be so designed and constructed that, if 
explosive rupture occurs at all, it shall be with a minimum of 
danger to attendants and surrounding objects. 

The prevention of liability to explosion, and the provision 
against danger should explosion actually take place, are the two 
directions in which to look for safety. 

As Fairbairn has remarked, the danger does not consist in 
the intensity of the pressure, but in the character and construc- 
tion of the boiler.^ Other things being equal, the boiler, or 
that form of boiler in which the original surplus strength of 
form and of details is greatest, and which is at the same time 
best preserved, is the safest. That class in which original 
strength is most certainly and easily preserved has an impor- 
tant advantage ; those boilers in which facilities for constant 
oversight, inspection, and repairs are best given are superior in 
a very important respect to others deficient in those points. 
For example, the cylindrical tubular boiler, if properly set, is 
very accessible in all parts, and may be at all times examined : 
it offers peculiar facilities for inspection and the hammer-test, 
and can be readily kept in repair ; but it is hable, in case of its 
becoming weakened by corrosion over any considerable area 
or along any extended line of lap, to complete disruptive ex- 
plosion. 

* Engineering Facts and Figures, 1865. 



,ii 



STEAM-BOILER EXPLOSIONS. 593 

On the other hand, the various ''sectional," or so-called 
'' safety," boilers are rarely as convenient of access or of 
inspection, and cannot usually be as readily and completely 
cleaned ; but they are so designed and constructed as to be 
little, if at all, liable to dangerous explosive rupture, and if a 
tube or other part bursts it is not likely to endanger life or 
property. That boiler is, therefore, on the whole, best which 
is least liable to those kinds of injury which lead to explosion^ 
and which is least likely to do serious harm should explosion 
actually take place. "^ Those who select the tubular boiler are 
commonly influenced mainly by considerations of cost and the 
first of the above considerations ; while the users of the water- 
tube sectional boiler are controlled by the second, in so far as 
either considers this form of risk at all. 

During the experiments of Jacob Perkins, about 1825 and 
later, the value of the " sectional " boilers, where high-pressures 
are adopted, was well shown. He frequently raised his steam- 
pressure to 100 atmospheres, t and in his earlier work rupture 
often took place, but no ill effects followed. The division 
of the boiler into numerous compartments saved the attendants 
from injury. In a letter to Dr. T. P. Jones, dated March 8, 
1827,:]: Mr. Perkins states that he had worked at the above- 
mentioned pressure with a ratio of expansion of 12; his usual 
pressure was about two thirds that amount, and the ratio of 
expansion 8. Mr. Perkins was then building an engine to 
safely carry a pressure of 2000 pounds per square inch.§ 

285. Defective Designs, causing explosion, are not as 
common as many other causes. They exist, however, more 
frequently than is probably usually supposed. The defects are 
generally to be observed in the staying of such boilers as re- 
quire bracing; in the insertion of the heads of plain cylindrical 
boilers; in the attachment of drums, and the arrangement of 

*Dr. E. Alban, following John Stevens, was probably the first to enunciate 
the principle, "so construct the boiler that its explosion may not be dangerous." 
The High-pressure Steam-engine, 1847, p. 70. 

f Jour. Franklin Inst., vol. iii., p. 415. 

X Ibid., p. 412. 

§ Reports on Steam-boilers, H. R., 1832, p. 188. 
38 



594 



THE STEAM-BOILER. 



man-holes and hand-holes; and, less frequently, in the selection 
of the proper thickness and quality of iron for shells and flues. 
Such defects as these are the most serious possible ; they 
are not only serious in themselves and at the start, but are 
of a kind which is commonly very certain to be exaggerated, 
and rendered continually more dangerous with age. A thin 
shell groAvs constantly thinner, a weak stay or brace weaker, 
and an unstayed head more likely to yield every day ; while a 
flue originally too thin is all the time overstrained, not simply 
by the steam-pressure, but also by the action of the relatively 
stronger parts around it. The most minute study of every 
detail and the most careful calculation of the strength of every 
part, with an allowance of an ample factor of safety, are the 
essentials to safety in design. 

Faulty design in bracing is illustrated by an explosion which 
took place in New York City, January 15, 1881, by which, for- 
tunately, however, no loss of life was caused. A dome-head, 
proportioned and braced as shown in the next figure, was blown 
out and tore up a sidewalk, under which the boiler was set, 




Fig. 133. — Dome akd Head. 



doing no other damage. The case was examined by Mr. 
Rose, who reported substantially as follows : 

The dome-crown tearing around the edge at A, also tore 
across at B^ being thus completely severed. The iron at the 
fractures was of excehent quality. The plate showed lamina- 
tion in places, and the crack around A was rusty, and evidently 



S TEA M-B OILE R EXPL O SI ONS. 



595 



not of recent formation. The six stays, three of which are 
shown in place at C, Fig. 133, were all in position in the dome, 
and their surfaces of contact with the dome were covered by a 
black pohsh, indicating movement and abrasion. 



^ 


. _ ^ 


~ -^^ 




^& 


1 ^^-....yllllBiM^ 


" 




m 




1 


fcjji 



Fig. 134. — Explosion of Dome. 

Apparently, as the pressure and temperature increased and 
decreased the dome-head might lift and fall, bending on A as a 
centre ; thus, taking / as a centre, the movement of C would 




Fig. 



-Defective Form. 



be in the direction of F, while at D the direction would be 
toward /, and the direction of motion of the two would nearly 




59^ THE STEAM-BOILER, 

coincide. The exploded dome shows an indentation at /, due 
to the motion of the foot of the stay. 

Another error in the design of this boiler is that the diameter 
of the dome-shell is 34 inches, and a circle of iron about 18 inches 
in diameter is punched out of the shell at D. This opening is 
required only to admit an inspector or workman to the interior 
of the boiler ; hence it is several inches wider than it should be. 

Defective design is illustrated in the case of the next boiler, 
the explosion of which left it in the form shown in Fig. 135.* 

This boiler consisted of two incompletely cylindrical shells, 
united as in the next figure, and ineffectively stayed at the 
lines of contact. This is a form which, 
insufficiently braced, becomes peculiarly 
dangerous. In the case illustrated, the 
Fig. 136.-JUNCT10X OF Shells, braccs yielded, after having been weak- 
ened by continual alteration of form, and split the two shells 
apart as seen. It is probably possible to brace boilers of this 
type safely, but it is better to avoid their use. They have some- 
times been used for marine purposes, where lack of space com- 
pelled special expedients, the bracing consisting of strong bolt,s 
with nuts and washers on the outside of the shell — a compara- 
tively strong and safe construction. 

Steam-domes are a source of some danger and of additional 
expense, however well designed and attached ; and it is proba- 
bly good economy, all things considered, to dispense with them 
altogether, using a dry pipe instead, and expending the amount 
of their extra cost on an increase in size of boiler over that 
which would have otherwise been selected. The large boiler 
will steam easier and more regularly, will give drier steam, and 
will be less liable to danger of deterioration or of explosion. 
A steam-drum above the boiler and connected by two separate 
nozzles, or a drum connecting the several boilers of a battery, 
is not subject to the objections which apply to the attached 
dome. 

286. Defective Construction, material, and workmanship 
are responsible for many explosions of steam-boilers. Thin, 

* Locomotive . Feb. 1880. 



STEAM-BOILER EXPLOSIONS. 59/ 

laminated, or blistered sheets, imperfect welds in bracing, the 
strain produced by the drift-pin, carelessness in the attachment 
of nozzles and drums, and in neglect of the precaution of 
strengthening man-holes and hand-holes, and bad riveting, are 
all common causes of weakness and accidents. Only the most 
careful and skilful, as well as conscientious, builders can be re- 
lied upon to avoid all such faults, and to turn out boilers as 
strong and safe as the designs may permit. 

In all cases, careful and unintermitted inspection by an ex- 
perienced, competent, and trustworthy inspector should be 
provided for by the proposing purchaser and user of the boiler. 
In the case of some of the more modern forms of boiler, con- 
structed under a system of manufacture which includes some 
machine fitting and working to gauge of interchangeable parts, 
with regular inspection before assemblage, this supervision be- 
comes less essential, and a careful test and trial, previous to 
acceptance, may be all that is necessary to insure a satisfactory 
and safe construction. Wherever defective material or bad 
workmanship is detected, the fault should always be corrected 
before the boiler is accepted, and previous to any trial or use 
under steam. Careless riveting and the use of the drift-pin are 
defects which cannot often be readily detected afterward, and 
they are such common causes of explosion that too much care 
cannot be taken to avoid any establishment of which the repu- 
tation in this regard is not the best. 




Fig. 137. — Defective Welding. 



Defective wields, the cause of many unfortunate accidents 
following the yielding stays or braces, are among the most 



59^ THE STEAM-BOILER. 

common and least easily detected of all faults. They are due 
to the difficulty of producing metallic contact in abutting sur- 
faces between which particles of scale and superficial oxidation 
may interpose. The grain of the iron, as illustrated in the ac- 
companying engraving, is broken at such junctions, and it is 
difficult to secure a good weld, and next to impossible to de- 
termine until it actually breaks whether it is seriously un- 
sound. 

Defective workmanship is often exhibited most strikingly 
by the distorted forms of rivets, revealed after explosion has 
caused a fracture along the seam, or when the yielding of the 
weakened seam has resulted in an explosion. The following' 
illustrations of a variety of cases of such distortion, all taken 
from a single boiler,* show how very serious this kind of de- 
fect may be. It is not to be presumed that such carelessness 
or worse, as is here exemplified, is to be attributed to the 
builder himself, but rather to the fault of workmen carefully 
concealing their action from the eye of the foreman or inspec- 
tor. No law or rule can protect the purchaser from this kind 
of fault; his only reliance must be upon the reputation of the' 
maker and his workmen, and the vigilance and skill of his in- 
spector. 

Fig. 138. — Rivet " driven" in overset holes, the conical 
point broken off by the tearing apart of the plates, the head 




Fig. 138. Fig. 139. 

nearly severed from the body, and probably weakened in 
" driving." 

Fig. 139. — Rivet "driven" in overset holes, head broken 
off by the tearing apart of the plates, conical point also nearly 

'^Locomotive, Feb. i88o. 



STEAM-BOILER EXPLOSIONS. 599 

broken off, bad sample of '' driving," cone too flat to properly 
hold down the plate. 

The next figure illustrates a group of similar distorted riv- 
ets which played their part in the production of an explosion. 



Fig. 140. — Defective Rivets. 



Fig. 141. — Rivet " driven" in slightly overset holes, point 
excentric and not symmetrical, too fiat to properly secure the 
edge of the plate. 

Fig. 142. — Rivet " driven" in badly overset holes, very weak. 




Fig. 141. Fig. 142. 

See Figs. 143, 144, 145, which were "sheared" at the time of 
the explosion. The dark shading on lower end. Fig. 142, indi- 
cates an old crack. 

Figs. 143, 144, 145. — Samples selected from a number taken 
from a " sheared " seam, which was believed to be the initial 
break from which the explosion arose. They were no doubt 
similar to Fig. 142 before they gave way. 



600 THE STEAM-BOILER. 

The Author, on one occasion, picked out with his fingers 




Fig. 143 



twelve consecutive rivets, deformed like those here illustrated, 
from a torn seam in an exploded boiler. 




Fig. 146. 

Fig. 146. — Rivet " driven" in overset holes ; it was probably, 
fractured under the head in driving. Taken from a seam that 
was broken through the rivet-holes. 




Fig. 147. 




Figs. 147 and 148. — Long rivets taken from a broken casting 
which they were intended to secure to the wrought-iron head 



STEAM-BOILER EXPLOSIONS. 6oi 

of the boiler. The holes in the wrought-iron plate were 
'* drifted " and chipped to allow the rivets to enter, as shown 
by -the enlarged portion of the body. This irregular upsetting 
and the sharp little wave of iron on the body of Fig. 147 indi- 
cate the thickness of the wrought-iron plate. 

287. Developed Weakness, usually a consequence of 
progressing decay by corrosion, is the most common of all 
causes of the explosion of steam-boilers. A boiler, designed and 
constructed of the best possible proportions and of the best of 
materials, having at the start a real factor of safety of six, 
may be assumed to be as safe against this kind of accident as 
possible ; but with the beginning of its life decay also begins, 
and the original margin of safety is continually lessened by a 
never-ceasing decay. The result is an early reduction of this 
margin to that represented by the difference between the work- 
ing pressure and that fixed as a maximum by the inspector's 
tests. Should this difference be sufficient to insure against ac- 
cident resulting from further depreciation in the interval be- 
tween inspector's or other tests, explosion will not occur ; 
should this margin not be sufficient, danger is always to be ap- 
prehended, and almost a certainty that rupture, and possibly 
explosive rupture, will at some time occur. This margin is, 
legally, usually fifty per cent ; it is too small to permit the pro- 
prietor to feel a real security. It is usually thought that the 
tests should show soundness under pressures at least double 
the regular working pressure at which the safety-valve is set."^ 
Many cases have been known in which the boiler has yielded 
at the working pressure not very long after the regular official 
inspection and pressure-test had taken place. 

Such an example was that of the explosion of the boiler of 
the Westfield, in New York Harbor, in June, 1871. 

The steam ferry-boat Westfield is one of three boats which 
have formed one of the regular lines between New York and 
Staten Island. The Westfield made her noon trip up from 

* Experiments made by the Author, and later by other investigators, have in- 
dicated the possibility that an apparent factor of safety of two, under load momen- 
tarily sustained, may not actually mean a factor exceeding one for permanent 
loading, — " Materials of Engineering," vol. i. , § 133; vol. ii., § 295. 



602 THE STEAM-BOILER. 

the island to the city on Sunday, July 30th, and while lying in 
the New York slip her boiler exploded, causing the death of 
about one hundred persons and the wounding of as many 
more. 

The boiler is of a very usual form, as represented in Fig. 
149, and is known as a "marine return-flue boiler." 

The diameter of its shell — the cylindrical part was ruptured 
— is ten feet ; its thickness, No. 2 iron, twenty-eight hundredths 
inch. 



Fig. 149. — Boiler of the Westfield. 

The evidence indicated that the explosion occurred in con- 
sequence of the existence of lines of channelling and long-exist- 
ing cracks, by which the boiler was gradually so weakened that, 
six weeks after its inspection and test, the pressure of steam 
being allowed by the engineer to rise slightly above the pres- 
sure allowed, the boiler was ruptured, giving way along a 
horizontal seam and tearing a course out of the boiler. 

The common lap-joint customarily adopted in the construc- 
tion of boilers is liable to such serious distortion under very 
heavy pressures as to produce leakage before actually yielding, 
and this leakage is sometimes so great as to act as a safety- 
valve. Thus, suppose a straight strip of plate riveted up in 
parts as in Fig. 150.^ A heavy pull will cause distortion as 
shown, in all cases except where a butt-joint is made with a 
covering strip on each side. If the metal is brittle and the 
rivet-heads strong, preventing the bending of the plate on the 

* See LocojHotive, Oct. 1880. 



S TEA M-B OILER EXPL SIGNS. 



603 



line of rivet-holes, the plate will probably break adjacent to G 
or F, Fig. 150; or in the middle, / and H. But should the 
plates be ductile or the rivet-heads weak, the break would occur 
at the line through the holes. 



D^EO C-l B Jd la GA 




If the plates. Fig. 150, A, etc., were straight at the joint, 
the extreme end, Z, must contract and the outer one expand at 
M, involving in the one a compression or upsetting, and in the 
other drawing the metal. If the joint be a butt, with a single 
outer cover, C, a similar contraction must take place at both ends, 
and a contraction of the middle of the covering strip, while the 
opposite would take place in the case of the joint with the inner 
cover, B. These distortions are not likely to take place in a 
transverse seam of a cylindrical boiler-shell from internal pres- 
sure. The butt-joint, with two covering plates, E, would re- 
tain its shape. 

Lapped longitudinal joints are shown at A' . Single-riv- 
eted and single-covered butts at B' and C . D' shows a double- 
riveted, single-covered butt. The next figures (151, i52)show 



M^ 



S 



Y <S))) 



Fig. i = 



()- 



<>- 



<)- 



<) 






H 




Y ^ 


T' 




% 




1 


1 




1^ 


i 




[^ "M 





P L 

Before Stretching. After Stretching. 

Fig. 152. 



the effect of strain on rivet-holes and on holes filled by the 
rivet. 

Multiple explosions are not infrequent. They usually occur 
in consequence of the explosion of one of a battery, with the 
result of injuring adjacent boilers in such manner that they also 



604 7' HE STEAM-BOILER. 

explode, the phenomena following each other so quickly as to 
produce the appearance of simultaneous explosion. It is pos- 
sible also that in some cases an accession of pressure in a set 
of boilers may take place with such suddenness as to explode 
several, notwithstanding there may exist a difference in their 
resisting power, the weakest not being given time to act as a 
safety-valve to the rest. It is doubtful, however, whether such 
cases can often if ever arise. 

288. General and Local Decay introduce vastly different 
degrees and elements of danger. As has been elsewhere stated, 
in effect, an explosion comes of extended rupture ; while local 
injuries or breaks, if they do not lead to wider injury, cannot 
cause widespread disaster. Hence, general corrosion, extend- 
ing over considerable areas of plate or along lines of considera- 
ble length, is a cause of danger of complete disruption and ex- 
plosion. A corroded spot in a firebox, a loosened rivet, or 
even a broken stay, if the boiler be otherwise well proportioned, 
well built, and in good order, may not be a serious matter; but 
a thinned sheet in the shell, a long groove under a lap, a line 
of loose rivets, or a cluster of weakened stays or braces, will 
certainly be most dangerous. General or widespread corrosion 
is very liable to lead to explosion ; local and well-guarded cor- 
rosion may cut quite through the metal, and simply cause a 
leak or an unimportant " burst." Old fireboxes are often seen 
covered with "patches" in places, and yet they very rarely ex- 
plode. Such a state of affairs may, nevertheless, by finally 
producing large areas of patched and fairly uniformly weak 
portions of the boiler, lead to precisely the conditions most 
favorable to explosion. A steam-boiler experimentally ex- 
ploded at Sandy Hook, N. J., September, 1871,^ had previ- 
ously, by repeated rupture by hydraulic pressure and patching, 
been gradually brought into precisely this state, and exploded 
under steam at 53I- pounds, — about four atmospheres pressure, — 
a slightly lower pressure than it had sustained (59 pounds) at its 
last test. On this occasion, when a pressure was reached of 
50 pounds per square inch, a report was heard which was prob- 

* Journal Franklin Institute, January, 1872. 



STEAM-BOILER EXPLOSIONS. 605 

ably caused by the breaking of one or more braces, and at 53J 
pounds the boiler was seen to explode with terrible force. The 
whole of the enclosure was obscured by the vast masses of 
steam liberated ; the air was dotted with the flying fragments, 
the largest of which — the steam-drum — rising first to a height 
variously estimated at from 200 to 400 feet, fell at a distance 
of about 450 feet from its original position. The sound of the 
explosion resembled the report of a heavy cannon. The boiler 
was torn into many pieces, and comparatively few fell back 
upon their original position. 




Fig. 153. — Corrosion. 

Thus corrosion may affect a single spot in a boiler, in which 
case a " patch," if properly applied, should make the boiler 
nearly as strong as when whole. A series of weak spots near 
each other may so weaken a boiler as to produce explosion, as 
may any considerable area of thin plate, although, when occur- 
ring in the stayed surfaces of a firebox, the metal may become 
astonishingly thin. A sketch of spots of corrosion is shown in 
Fig. 153, which represents the cause of an actual explosion. 
This cause of explosion may be either internal or external, 
and is induced internally by bad feed-water, and externally by 
dampness or by water leaking from the boiler, either unseen or 
neglected. It is always dangerous to have any portion of a 
boiler concealed from frequent observation. 

The effect of covering a part of a sheet subject to corrosion 
by solid iron, as by the lap of a seam, is shown in the next fig- 
ure, which also exhibits a common method of corrosion along a 
seam. The same effect is seen still more plainly in the sue- 



6o6 



THE STEAM-BOILER. 



ceeding figure, in which the pitting which so often attends the 
use of the surface-condenser is also well shown. 

289. The Methods of Decay are as various as the forms 
and location of the parts subject to corrosion. As Colburn* has 
said : '^ As a malady, corrosion corresponds, in its comparative 
frequency and fatality, to that great destroyer of human life, 
consumption ;" and it has as innumerable phases and periods of 
action. The two most common methods of decay are the gen- 
eral, and here and there localized, corrosion that goes on in all 
boilers, and in fact on all iron exposed to air and carbonic acid, 
in presence of moisture ; and the concentrated and localized oxi- 






FiG. 154. — Corrosion at a Seam. 



Fig. 155.—" Pitting.' 



dation that is often seen along the line of a seam at the edge of 
the lap, where the continual changing of form of the boiler is as 
constantly producing an alternate flexing and reflex motion of 
the sheet, which throws off the oxide as fast as formed along 
that line, and exposes fresh, clean metal to the corroding influ- 
ence. A groove or furrow is thus in time produced, which 
may, as occurred in the case of the Westfield (Fig. 149), actually 
cut through the sheet before explosion takes place. 

The phenomenon known as "■ grooving" or " furrowing" is 
well illustrated by the case just mentioned, in which this action 
was originally started, probably, by the carelessness of the work- 
man, who, either in chipping the edge of the lap along a girth- 



* Trans. Brit. Assoc, il 



STEAM-BOILER EXPLOSIONS. 



607 



seam, or in calking the seam, scored the under-sheet along the 
edge of the lap with the corner of his chisel or with the calk- 
ing-tool. This is a very common cause of such a defect. 

The boiler was broken into three parts. The first, and by 
far the largest part, consisted of the furnaces, steam-chimney 
and flues, with a single course of the shell ; the second con- 
sisted of two courses of the outside of the shell next the back- 
head, together with that head, to which they remained attached ; 
the third piece consisted of a single complete course from the 
middle of the cylindrical shell, which was separated at one of 
its longitudinal seams, partially straightened out and flung 
against the bottom and side of the boat. This last piece re- 
mained opposite its original position in the boiler before the 
explosion, while the first and second pieces went in opposite 
directions, the former finally lying several feet nearer the en- 
gine than when in situ, and against the timbers of the " gallows- 
frame," while the latter piece was thrown fifty feet forward into 
the bow of the boat, where it fell, torn and distorted. The 
longitudinal seam, along which piece number three separated, 
and the deep score or " channel " cutting nearly through in many 
places, and presenting every evidence of being 
an old flaw, were plainly seen. The mark 
made by a chisel in chipping, and that of the 
calking-tool, were seen, and indicated the 
probable initiative cause of the flaw. 

The Author examined this piece and 
found an old crack or " channel " cut along 
the edge of the horizontal lap referred to as 
being at the ends of the sheet, and in some 
places so nearly through that it was dif^cult 
to detect the mere scale of good iron left, 
while in other places there remained a six- 
teenth of an inch of sound metal. Fig. 156 
exhibits a section of the crack. 

Were this the weakest place in the boiler, and the least thick- 
ness here one sixteenth of an inch, the tensile strength being 
equal to the average determined by the tests made of the iron, the 
pressure required to rupture such a boiler, ten feet in diameter, 




Fig. 156. 



6o8 THE STEAM-BOILER. 

would be 44079 X iV >< ^ "^ 120 = 47 pounds per square inch, 
nearly. A pressure of 27 or 28 pounds would burst it open 
where the least thickness was slightly more than one thirty- 
second of an inch. One portion may be supported, to some 
extent, by a neighboring stronger part. Along this longitudi- 
nal seam the limit of strength would seem to have been about 
30 pounds per square inch, which is about the pressure at 
which the boiler exploded, this seam ripping for a distance of 
several feet. The original strength of the boiler was equal to 
about 120 pounds along the horizontal seams, — its then weak- 
est parts, — provided that the iron had, when new, the average 
strength of the specimens which we have tested. In the ver- 
tical seams may be seen, in some places, similarly weakened 
portions, the cracks running usually from rivet to rivet, and 
here and there exhibiting marks that show the wedging action 
of the '' drift-pin," and many places, both in longitudinal and 
girth-seams, are cut by the chisel and marked by the '' calking- 
tool." 

These lines of " furrowing" are sometimes continuous, and 
sometimes interrupted by portions of good iron. They are 
probably in most cases caused by changes in form of the boiler 
with variations of temperature and pressure, some line of local 
weakness determining the line along which the plate shall bend, 
and this bending taking place continually, though ever so 
slightly, along the same line precisely, finally produces rupture. 
This change of form of the shell of a boiler may be due to 
either the constantly occurring variation of pressures, as steam 
is made or is blown off during working hours ; or it maybe pro- 
duced by changes of temperature. Large and thin boilers are 
especially liable to this form of injury. Bad methods of sup- 
port may permit or may cause variations of form and this defect, 
which is all the more dangerous that it is difficult in many cases 
to detect it. Water trickling from leaks sometimes causes a 
kind of grooving along its path, hardly less serious in its nature 
and extent. 

Sometimes this action produces a narrow crack, and at other 
times, as above stated, as the rust formed is thrown or scoured 
off the iron at the bend, leaving a comparatively clean surface. 



STEAM-BOILER EXPLOSIONS. 609 

oxidation is probably accelerated, and the fault takes the form 
of a groov^e or furrow. If unperceived, this goes on until a rup- 
ture or an explosion occurs. 

Of forty explosions of locomotive boilers noted in British 
Board of Trade reports,^ eighteen gave way at the firebox and 
twenty at the barrel. Of these twenty, every one was the re- 
sult of ''grooving" or cracks along the lap of seams, all of 
which were lap-joints. The grooves were most common ; they 
ahvays occurred along the edge of the inside overlap, just w^here 
the changes of form with varying pressure would concentrate 
their effects/ Such results are sometimes also seen at butt- 
joints, especially where a strip has been used inside. The rack- 
ing action of the engines may produce precisely the same effect. 
Wherever change of form is felt, grooving or furrowing and 
cracking may be expected to be found in time. Where the 
boiler is already heavily strained along one of these lines of re- 
duced thickness, any slight added stress, as a jar, or the action 
of a calking-tool, as when leaks in boilers under pressure are 
being calked, may precipitate an explosion, the break follow- 
ing the groove or crack just as a stretched drum-head may yield 
to the scratch of a knife. 

290. Differences in Temperature between parts of a 
boiler more or less closely connected in the structure may pro- 
duce serious strains, and some instances of explosion have been 
attributed to this cause. 

Changes of temperature occur as steam is raised or blown off 
from a boiler, and its temperature becomes at one time that due 
the steam-pressure, and then it falls to that of the atmosphere 
each time steam is blown off. It will change its form more 
or less, and will usually be subjected to some strain by this pro- 
cess. Again, while actually at work, the steam-space and upper 
portion of the water-space are at the temperature of steam at 
the working pressure, while the lower part is continually vary- 
ing in temperature from that of the feed-water to the maximum 
which it attains after entrance. This difference of temperature 

* " Wear and Tear of Steam-boilers." F. A. Paget, Trans. Soc. of Arts, 1865 ; 
London, 1865, p. 8. 

39 



6lO THE STEAM-BOILER. 

between the upper and lower parts of the boiler, as well as be- 
tween other portions, causes a continual tendency to distortion; 
and if this distortion be resisted, a stress is thrown upon the 
parts equal to that which would be required, acting externally, 
to remove the distortion, if produced. The stress is also equal 
to the mechanical force that would be necessary to produce 
similar distortion. 

Thus, had the temperature of the main and upper part of 
the Westfield's boiler been, after the entrance of the feed- 
water, 273°, or that due to about twenty-seven or twenty-eight 
pounds steam, while the feed-water had a temperature of 73°, 
the bottom of the boiler having a temperature, in consequence, 
200° below that of the top, the difference in length would be 
about one eight-hundredth, and, if confined by rigid abutments, 
iron so situated would be subject to a stress of twelve and a 
half tons per square inch. But in this case one part would 
yield by. compression and the other by extension, and if they 
were to yield equally it would reduce the stress to six and a 
quarter tons. Actually, in this case, the lower fourth and upper 
three fourths would be more likely to act against each other^ 
and the stress, if the boiler had no elasticity of form, would be 
about nine tons. Any elasticity of form — and boilers generally 
possess considerable — would still further reduce the strain, and 
it very frequently makes it insignificant. 

It is thought, by some experienced engineers and other 
authorities, that many of the explosions known to have taken 
place, after inspection and test, at pressures lower than those of 
the test, are caused by the weakening action of unequal expan- 
sion, the stresses and strains produced in this manner being 
superadded to those due to simple pressure, against which latter 
the boiler might otherwise have been safe. Such effects may 
also be the final provocative to explosion when cold feed-water 
is pumped into a boiler, on getting up steam, or possibly, some- 
times, when cooling off. It has even been asserted that an 
empty boiler has been ruptured by such changes of form conse- 
quent on building a light fire of shavings in a flue to start the 
scale. The Author has known of instances in which the girth- 
seams of large marine flue-boilers were ruptured along the line 



STEAM-BOILER EXPLOSIONS. 6l I 

of rivet-holes a distance of several feet by the introduction of a 
large volume of cold feed-water, when steam was up, but the 
engine at rest. 

The differences of temperature on the two sides the sheet 
may be important. While it is true that the heat supplied by 
the furnace-gases is absorbed by the boiler to the same extent, 
practically, without much regard to the thickness of the plates 
of the boiler, it is a well-known fact that the resistance of iron 
to the flow of heat is so great that the effect of heat on the 
metal itself is seriously modified by the thickness of the sheet. 
Heavy plates '' burn" away, projecting rivet-heads are destroyed, 
and the laps of heavy plates are especially liable to be thinned 
seriously where they are employed. 

A variation of temperature of considerable range, and often 
recurring, frequently causes injury by hardening the metal of 
the boiler, making it brittle and liable to crack with change of 
form, and also produces the very change of form causing this 
cracking. 

The experiments of Lt.-Col. Clark, R.A.,* show that great 
distortion may be thus produced. It is probably thus that iron 
and especially steel fireboxes so often crack, in consequence of a 
continual swelling of the metal under varying temperatures and 
the stresses so caused. This action, combined with oxidation, 
external and internal, sometimes makes the sheets and oftener 
the stays of a boiler remarkably weak and brittle ; they some- 
times become more like cast than wrought iron. The thicker 
the sheet, the more readily is it overheated and overstrained. 

The extent to which alteration of form under pressure may 
go, with good material, before actual rupture, is illustrated by 
the following:! During the summer of 1868, a cylindrical boiler, 
made of ^-inch steel plates, built at the Fort Pitt Iron Works, 
Pittsburg, was tested under authority of the government, with 
a view to determining the relative advantages of steel and iron 
as a material for navy boilers. When the pressure of cold water 
had reached 780 pounds, the girth of the boiler was found to 

* Proc. Royal Society, 1863; Journal Franklin Institute, 1863. 
f Iron Age, Sept. 26, 1872. 



6l2 THE STEAM-BOILER. 

have permanently increased 3f inches, and at 820 pounds rup_ 
ture occurred. 

Cases have been known in which a steel crown-sheet has be- 
come overheated, and has sagged down until, the tube-sheet 
going with it, a basin-shaped form has been produced, convex 
toward the fire, and yet no fracture produced, even when the 
pump was put on and the boiler filled up again under pressure. 

291. The Management of the Steam-boiler, or, more 
correctly, its mismanagement, while in operation, and a neglect 
of proper supervision and inspection, may be considered, on 
the. whole, the usual reason of explosion, as the deterioration 
of the boiler is the immediate cause; and this deterioration is 
almost invariably so gradual and so readily detected by intel- 
ligent and painstaking examinations that there is rarely any 
excuse for its resulting disastrously. A well-made boiler under 
good management and proper supervision may be considered 
as practically free from danger. 

The person in direct charge of the boiler is usually a pre- 
sumably experienced and trustworthy^ man. He should be 
thoroughly familiar with his business, generally intelligent, of 
good judgment, ready and prom.pt in emergencies, and abso- 
lutely reliable at all times. His first duty is to see that the 
boiler is full to the water-line, trusting only the gauge-cocks ; 
he must keep constant watch of the furnaces, flues, and other 
surfaces subject to the CcCtion of the fire, and thus be certain 
that no injury is being done by overheating or sediment ; he 
must keep the feed-apparatus in perfect working order, keep up 
the supply of water continuously and regularly, and see that 
the safety-valve is in good order at all times. Such careful 
management, conscientious inspection and cleaning, and repair- 
ing at proper intervals will insure safety. 

To keep the safety-valve in good working order and to make 
certain that it is operative, provision should be made for 
opening it by hand, and it should be daily raised, before getting 
up steam, to the full height of its maximum lift. 

Explosions of Gas sometimes precipitate steam-boiler explo- 
sions. Should the gases leaving the fuel and the furnace not 
be completely burned, but become so mingled in the flues as to 



\\ 



STEAM-BOILER EXPLOSIONS. 613 

produce an explosive mixture, combustion finally occurring, the 
shock may be sufficient to cause rupture of the boiler, and, as 
has actually sometimes happened, its explosion. Sewer-gases 
have been known to find their way into an empty boiler 
through an open blow-off pipe, and have been exploded by the 
first light brought to the man-hole, and with serious damage to 
adjacent property. Mineral oils used to detach scale have 
caused similar dangerous and sometimes fatal explosions by the 
ignition of the mixture of their vapors and the air within the 
boiler. It is important that care be taken in using lights about 
boilers in such cases of application of mineral oils. 

Explosions of gas within a boiler at work cannot occur ; but 
the suggestion of the possibility of such an occurrence is often 
made. No decomposition of water can take place except a 
portion of the boiler is overheated ; this happening, all the 
oxygen produced is absorbed by the iron, and no recombination 
can occur later, even were it possible for ignition to take place 
under the conditions producing decomposition. 

The flooding of a boiler with water until it is filled to the 
steam-pipe or safety-valve may cause so serious a retardation of 
the outflow of the mingled fluids as to result in overpressure 
and great danger. Mr. W. L. Gold "^ gives the following 
instances, and the experience of the Author justifies fully his 
statement. The steam-pipe or the safety-valve cannot relieve 
a full boiler rapidly and safely. 

First, a boiler 38 inches in diameter, two flues, shell \ inch 
Juniata iron, ruptured in the sheet a crack 9 inches long, steam- 
gauge indicating 60 pounds, safety-valve weighted at 80 pounds 
pressure. This rupture closed instantly ; and if he had not seen 
it made, he might possibly have been surprised by an explosion, 
with water and steam in their normal condition, very shortly 
after. Second, a steam-drum (spanning a battery of five 
boilers) 30 inches in diameter. The blank-head forced (bulged) 
out \\ inches, the stay-rods stretched, and the corner of the 
head-flange cracked one third around. Third, a vertical boiler, 
built especially to carry high pressure (safe running pressure 

* Am. Manufacturer , Feb. 1881. 



6i4 



THE STEAM-BOILER. 



150 pounds), the hand-hole and man-hole joints forced out past 
the flanges, the steam-pipe joints and union forced out, the 
packing in the engine-piston destroyed, and the engine gener- 
ally racked, so as to be almost useless. Steam-pressure by 
gauge from 40 to 60 pounds ; safety-valve weighted at 90 
pounds. 

Mr. Gold suggests that, as this is a not infrequent occur- 
rence, many explosions may be simply the final act in the 
drama commenced by the feed-pump. 

292. Emergencies must be met with a clear head and 
ready wit, with perfect coolness, and usually with both prompt- 
ness and quickness of action. Every man employed about 
steam-boilers, as well as every engineer and every proprietor,, 
should have carefully thought out the proper course to take in 
any and every emergency that he can conceive of as likely or 
possible to arise, and should have constantly in mind the means 
available for meeting it successfully. When the time comes to 
act, it is not always, or even often, possible to take time to study 
out the best thing to be done ; action must be taken, on the 
instant, based on earlier thought or on either the intuition or 
the impulse of the moment. 

*' Low-zvatcr' presents perhaps the most common, as well 
as one of the most serious, of such emergencies. The instant 
it is detected, the effort must be made to check the fall to a 
lower level ; the fire must be dampened, preferably by throwing 
on wet ashes, and the boiler allowed to cool down. Care 
should be taken that the safety-valve is not raised so as to pro- 
duce a priming that might throw water over the overheated 
metal, and that no change is made in the working of either en- 
gine or boiler that shall produce foaming or an increased pres- 
sure. If. on examination, it is found that the water has not fallen 
below the level of either the crown-sheet or any other extended 
area of heating-surface, the pump may be put on with perfect 
safety; but if this certainty cannot be assured, the boiler should 
be cooled down completely, and carefully inspected and tested,, 
and thoroughly repaired if injured^ If no part of the exposed 
metal is heated to the red heat there is. no danger, except from 
a rise in the water-level and flooding the hot iron. If any por- 



STEAM-BOILER EXPLOSIONS. 615, 

tion should be red-hot, an additional danger is due to the 
steam-pressure, which should be reduced by continuing the en- 
gine, in steady working while extinguishing the fire. If the 
safety-valve be touched at such a time, it should be handled 
very cautiously, allowing the steam to issue very steadily and 
in such quantities that the steam-gauge hand shows no fluctua- 
tion, while slowly falling. The damping of the fire with wet 
ashes will reduce the temperature and pressure very promptly 
and safely. The Author has experimentally performed this 
operation, standing by a large outside-fired tubular boiler while 
all the water was blown out, and then covering the fire. The 
pyrometer inserted in the boiler showed no elevation of tem- 
perature until all the water was gone, and the fire was then so 
promptly covered that the rise was but a few degrees, and the 
boiler was not injured. As it proved, there was not the slight- 
est danger in that case ; but with less promptness of action 
some danger might have arisen of injury to the boiler, although 
probably not of explosion. 

Overheated plates, produced by sediment, or over-driving, 
resulting in the production of '^ pockets" or of cracks, are, virtu- 
ally, cases of low-water, and the action taken should be the same. 
The boiler being safely cooled down, the injured plate should 
be replaced by a sound sheet, all sediment or scale carefully re- 
moved, and a recurrence of the causes of the accident effectively 
provided against. 

Cracks, suddenly appearing in sheets exposed to the fire, or 
elsewhere, sometimes introduce a serious danger. The steps to 
be taken in such a case are the immediate opening of the safety- 
valve and reduction of steam-pressure as promptly and rapidly 
as possible, meantime quenching the fire and then cooling off 
the boiler and ascertaining the extent of the injury, and repair- 
ing it. In such a case, unless the crack is near the safety-valve 
itself, no fear need be entertained of too rapid discharge of the 
steam. 

Blistered sheets should be treated precisely as in the cases 
preceding. It is not always possible to surmise the extent of 
the injury or the danger involved until steam is off and an ex- 
amination can be made. It is not, however, absolutely neces- 



6i6 



THE STEAM-BOILER. 



sary to act as promptly as in the preceding cases; an 
the blister is not large and is not extending, it is sometimes 
perfectly allowable to await a convenient time for blowing off 
steam and making repairs. 

An inoperative safety-valve, either stuck fast, or too small to 
discharge all the steam made, or to keep the pressure down, to 
a safe point, produces one of the most trying of all known emer- 
gencies. In such a case steam should be worked off through 
the engine, if possible, and discharged through any valves 
available, through the gauge-cocks, or even through a few scat- 
tered rivet-holes, out of which the rivets may be knocked on 
the instant ; the fire being meantime checked by the damper 
or by free use of water. The throwing of water into a furnace 
is often a somewhat hazardous operation, however, and if neces- 
sary, should be performed with some caution, to avoid risk of in- 
jury of either the person attempting it, or of the boiler. The 
use of wet ashes is preferable. In all cases in which it is to be at- 
tempted to reduce the rate of generation of heat, closing the ash- 
pit doors as well as opening the fire-doors will be of service by 
checking the passage of hot air from below and accelerating ' 
the influx of cold air above the grate ; but the closing of the 
ash-pit involves, with a hot fire, some risk of melting down the 
grates. 

293. The Results of Explosions of steam-boilers, in 
spreading destruction and death in all directions, are so famil- 
iar as scarcely to require illustration ; but a few instances may 
be described as examples in which the stored energy of various 
types of boiler has been set free with tremendous and impres- 
sive effect. 

Referring to the table in ^ 269, and to case No. i : The explo- 
sion of a boiler of this form and of the proportions here given, 
in the year 1843, ii"^ the establishment of Messrs. R. L. Thurston 
& Co., at Providence, R. I., is well remembered by the Author. 
The boiler-house was entirely destroyed, the main building 
seriously damaged, and a large expense was incurred in the pur- 
chase of new tools to replace those destroyed. No lives were 
lost, as the explosion fortunately occurred after the workmen 
had left the building. A similar explosion of a boiler of this 



STEAM-BOILER EXPLOSIONS. 617 

size occurred some years later, within sight of the Author, which 
drove one end of the exploding boiler through a 16-inch wall, 
and several hundred feet through the air, cutting off an elm- 
tree high above the ground, where it measured 9 inches in di- 
ameter, partly destroying a house in its further flight, and fell 
in the street beyond, where it was found hot and dry immedi- 
ately after striking the earth. Long after the Author reached 
the spot, although a heavy rain was falling, it was too hot 
to be touched, and was finally, some time later, cooled off by a 
stream of water from a hose, in order that it might be moved 
and inspected. It had been overheated, in consequence of low- 
water, and cold feed-water had then been turned into it. The 
boiler was in good order, but four years old, and was considered 
safe for no pounds. The attendant was seriously injured, and 
a pedestrian passing at the instant of the explosion was buried 
in the ruins of the falling walls and killed. The energy of this 
■explosion was very much less than that stored in the boiler 
when in regular work. 

A boiler of class No. 3, which the Author was called upon 
to inspect after explosion, had formed one of a '' battery" of 
ten or twelve, and was set next the outside boiler of the lot. Its 
explosion threw the latter entirely out of the boiler-house into 
an adjoining yard, displaced the boiler on the opposite side, 
and demolished the boiler-house completely. The exploding 
boiler was torn into many pieces. The shell was torn into a 
helical ribbon, which was unwound from end to end. The fur- 
nace-end of the boiler flew across the space in front of its house, 
tore down the side of a '* kier-house," and demolished the kiers, 
nearly killing the kier-house attendant, who was standing be- 
tween two kiers. The opposite end of the boiler was thrown 
through the air, describing a trajectory having an altitude of 
fifty feet and a range of several hundred, doing much damage 
to property en route, finally landing in a neighboring field. The 
furnace front was found by the Author on the top of a hill, a 
quarter of a mile, nearly, from the boiler-house. The attendant, 
who was on the top of the boiler at the instant of the explo- 
sion, opening a steam-connection to relieve the boiler, then con- 



6l8 THE STEAM-BOILER. 

taining an excess of steam and a deficiency of water, was 
thrown over the roof of the mill, and his body was picked up 
in the field on the other side, and carried away in a packing- 
box measuring about two feet on each side. The cause was 
low-water and consequent overheating, and the introduction of 
water without first hauling fires and cooling down. Both this 
boiler and the plain cylinder are thus seen to have a projectile 
effect only to be compared to that of ordnance. 

The violence of the explosion of the locomotive boiler is 
naturally most terrible, exceeding, as it does, that of ordnance 
fired with a charge of 1 50 pounds of powder of best quality, or 
perhaps 250 pounds of ordinary quality fired in the usual way."^ 
On the occasion of such an explosion which the Author was 
called upon to investigate, in the course of his professional prac- 
tice, the engine was hauling a train of coal cars weighing about 
1000 tons. The steam had been shut off from the cylinders a 
few minutes before, as the train passed over the crest of an in- 
cline and started down the hill, and the throttle again opened 
a few moments before the accident. The explosion killed the 
engineer, the fireman, and a brakeman, tore the firebox to 
pieces, threw the engine from the track, turning it completely 
around, broke up the running parts of the machinery, and made 
very complete destruction of the whole engine. There was no 
indication that the Author could detect of low-water ; and he 
attributed the accident to weakening of the fire box sheets at 
the lower parts of the Avater-legs by corrosion. The bodies of 
the engineer and fireman were found several hundred feet from 
the Avreck, the former among the branches of a tree by the side 
of the track. This violence of projection of smaller masses 
would seem to indicate the concentration of the energy of the 
heat stored in the boiler, when converted into mechanical en- 
ergy, upon the front of the boiler, and its application largely to 
the impulsion of adjacent bodies. The range of projection was, 



* The theoretical effect of good gunpowder is about 500 foot-tons per pound 
(340 tonne-metres per kilogramme), according to Noble and Abel. 



STEAM-BOILER EXPLOSIONS. 



619 



in one case, fully equal to the calculated range. The energy 
expended is here nearly the full amount calculated. 

Figs. 157, 158, 159. 160 illus- 
trate the explosion of two large boil- 
ers which produced very disastrous 
effects,* killing the attendant and de- 
stroying the boiler-house and other 
property. These boilers were hori- 
zontal, internally-fired, drop-flue boil- 
ers, seven feet diameter and twenty- 
one feet long, the shells single-riv- 
eted, originally five sixteenths of an 
inch thick. 

The two exploded boilers were 
made twenty-one years before the 
explosion, and worked, as their mak- 
ers intended, at about thirty pounds 
per square inch, till about twenty 
months before the explosion, at which 
time additional power was required, 
and the pressure was increased to and limited at fifty pounds. 

A third boiler did not explode, but was thrown about fifty 
feet out of its bed. 




Fig. 



—Explosion of Boilers at 
Brooklyn, N. Y. 




Fig. 158.— Position of the Three Boilers after the Explosion. 

A few minutes before noon, while the engine was running at 
the usual speed, the steam-gauge indicating forty-seven pounds 

* Scientific American, May 20, 1882. 



620 



THE STEAM-BOILER. 



pressure, and the water-gauges showing the usual amount of 
water, the middle one exploded : the shell burst opt-n, and was 
nearly all stripped off. The remainder of the boiler was thrown 
high in the air. 

While this boiler was in the air. No. i, the left-hand boiler, 
having been forcibly struck by parts of No. 2, also gave way so 




Fig. 159. — Initial Rupture. 

that its main portion was projected horizontally to the front, 
arriving at the front wall of the building in time to fall under 
No. 2, as shown in Fig. 158. The most probable method of rup- 
ture is indicated in Fig. 159, as the line AB separates a ring of 
plates which was found folded together beneath the pile of d^- 




FiG. 160. — Interior of Boiler-house Prior to the Explosion. 

bris. If the initial break had been at some point on the bot- 
tom, this belt of plates would have been thrown upward and 
flattened, instead of downward, where it was thrown by the flood 
of water from No. i boiler. 

The third boiler was raised from its bed by the issuing water, 
and thrown about fifty feet to the right of its original position. 



STEAM-BOILER EXPLOSIONS. 



621 



These two boilers contained probably more than fourteen 
tons of water, which had a temperature due to forty-seven 




Fig. 161.— Exploded Locomotive. 



pounds of steam, and the effect of its sudden liberation was 

equal that of several hundred pounds of exploded gunpowder. 

The terrible wreck usually consequent upon the explosion 




Fig. 162. — Tubes of an Exploded Boiler, 



of a locomotive boiler is well illustrated in the accompanying 
engraving, which represents the results of such an explosion on 
the Fitchburg Railway, August 13, 1877: while the havoc 



I 



622 



THE STEAM-BOILER. 



wrought among the tubes on such occasions is as strikingly 
illustrated in Fig. 162. 

In the case of an explosion of a locomotive investigated by 
a commission of which the Author was a member, the train was 
moving slowly when the boiler exploded with a loud report ; 
the locomotive was turned completely over backward, carrying 
with it and burying the fireman beneath the ruins. 

Nothing could at first be found of the engineer. Parties 
searched for long distances about the wreck for signs of the un- 
fortunate man, but it was not until next morning that his body 
was found. It was discovered lying in the woods, seven hun- 
dred feet away from the locomotive. 

The locomotive was completely demolished, and every part 
of the machinery was twisted or broken into pieces. The track 
was torn up for some distance, and rails were bent like coils of 
rope. The firebox of the locomotive was hurled from its posi- 
tion and broken into many pieces. A large piece weighing 
many hundred pounds was carried five hundred feet. The 
dome and sand-box were thrown an eighth of a mile into the 
adjacent river. The wheels ot the engine were torn off, and no, 
one piece of the cab was discovered. The engineer bore an 
excellent reputation as being a careful man, always carrying a 
large supply of water. The engine was one of approved make, 
and had been in use for fifteen years. It had just come from the 
repair-shop. A new firebox had been put in three years before, 
and the boiler was thoroughly examined about six weeks earlier. 
The iron was in many cases twisted and bent into shapeless rolls. 
The point of rupture was apparently in the left-hand lower cor- 
ner of outside shell of the firebox. The cause was variously as- 
signed as a percussion or '^ fulminating" action due to overheated 
iron and to certain defective portions of the firebox. The latter 
was probably the true cause. 

The following may be taken as another illustration of the 
tremendous effects of explosion at usual working pressure, with 
an ample supply of water: A boiler of the locomotive type was 
constructed for use in a small steamer. Its shell was of iron, 4 
feet in diameter, and j^^-ths inch thick. It was ''tested" by 
filling with water and raising steam. It exploded with the 



I 



STEAM-BOILER EXPLOSIONS. 623 

safety-valve set at 120 pounds pressure per square inch, blow- 
ing freely, although held down by the man in charge, and killed 
and injured several people. The hiss of steam escaping from the 
initial rupture was heard an instant before the explosion. The 
boiler was turned end for end, and the firebox torn from the 
boiler in two pieces, one being carried to a distance of about 
500 feet and imbedded in the mud of a canal-bed ; the other por- 
tion, weighing about 4800 pounds, was carried a distance of be- 
tween 400 and 500 feet, and crashed into the side of a building 
filled with sash, blinds, and doors piled closely together. This 
piece of iron comprised the firebox, the dome, and the end of 
the boiler, and was straightened into a piece 30 feet long and 
four feet wide. This piece is said to have rushed through the 
air with a whirling motion until it struck the building. It cut 
the side of the building and beams and rafters like straws, push- 
ing the front of the building forward several feet. Fragments 
of the boiler were found at many points considerably distant 
from the scene of the explosion, and in many places windows 
were shattered by the concussion. 

The shell of the boiler was reversed by the force of the 
explosion, with such force that one end was buried four feet . in 
the road-bed. All the flues remained in the boiler, one end of 
which was torn from them while the other remained in place. 
At the instant of the explosion the air for many feet in every 
direction was filled with flying fragments, many of them being 
thrown to a great height. 

In one case coming under the observation of the Author, a 
locomotive set as a stationary boiler gave way in the firebox, 
and let out the water and steam, but injured no one. The rent 
was about twelve inches long and eight inches wide. The iron 
in that place was weakened by corrosion, otherwise the boiler 
was in good condition. Repairs were immediately commenced 
and the boiler was ready for use next day. Had this rent oc- 
curred at or above the water-level, it is very possible that an 
explosion may have resulted, in the manner suggested by Clark, 
and Colburn. 

In an explosion of a tubular boiler at Dayton, O., Oct. 25, 



624 THE STEAM-BOILER. 

i88i,"^ by which several Hves and much property were destroyed^ 

the rupture started along the lap 
AB in the figure, and was evi- 
dently due to the furrowing which 
had been there, in some way, pro- 

^P^^^^ II I 1 duced. The boiler was less than 

^^^^^^^^^^^^^^^ a year old, and was reported to be 
V^ ^i^«^ , ,!;. '^ ^=s^-zzir-^ ^ of good material and workman- 
ship. The longitudinal seams were 
double-riveted, and it is very pos- 
sible that the stiffness thus .pro- 

FiG. 163. — Initial Rupture; "Grooving." , , , - . ,. , 

duced along their Imes may nave 
so localized the strains due to alterations of form as to have led 
to this fatal result, aided by the action of the calking-tool, the 





Fig. 164. — Boiler-explosion at Dayton, Ohio. 

marks of which along the line at which the crack gradually 

worked through the sheet were plainl)^ 
visible. The boiler had, when first set 
in place, been tested to 140 pounds; 
the explosion occurred at probably less 
than 80. 

A strip of plates, as in Fig. 165, was 
torn from the boiler, separating it into 
two parts, as seen in the two succeeding 

figures, and throwing them apart with all the force due to a 

* Scientific American, Dec. 17, 1881. 




Fig. 165.— Girdle of Plates torn 
from No. 2 Boiler. 



STEAM-BOILER EXPLOSIONS. 



625 



hundred millions of foot-pounds of available stored heat-energy,, 
and entirely destroying the house in which they were set. 

In a case of explosion at Pittsburg, Pa., in December, 
1 88 1, a battery of flue-boilers was connected, as seen in Fig. 




Fig. i66a. 

Rear End of Boiler 

AFTER Explosion. 



Fig. i66<5. 
Rear End of Boiler be- 
fore Explosion. 



Fig. 167. — Front End of Boiler 
.A.FTER Explosion. 



169, by steam-drums above the nearer two and mud-drums 
beneath all three. The steam -pressure was not far from 125 
pounds per square inch at the time of the accident. The boilers 




5.— Principal part of No. 5 boiler, thrown over the church on the bluff. 6.— Principal part of No. 6 boiler. 
Fig. i68.— Explosion of Two Steam-boilers at Pittsburg, Pa. 

were fifteen years old, but had been tested to 170 pounds two 
years earlier, and allowed to work at 120 pounds, although they 
had been repeatedly patched and repaired.* The rules of the 



* Scientific American^ Feb. 4, 18S2. 



40 



626 



THE S TEA M-B OILER. 



insurance companies would have allowed but one fialf this 
pressure. 

The strains produced by the changes of form with varying 
temperature of feed-water, and by the action of the new iron of 
the patches on the older and corroded parts of the boiler, 
started cracks which gradually weakened them, and finally led 




Fig. 169.— Under Sides of Boilers. 

to a rupture along the worst line of injury, AB^ in the preced- 
ing figure, opening the course of plates at a, and tearing it out 
as in the next figure, in which AB is the line of initial fracture. 



mA 


4^ 


f"^^ 






■' ' '/'r 



Fig. 170. — Course of Plates Detached. 



The destruction of this (No. 6) boiler was accompanied by the 
disruption of that next it (No. 5), which was also in about as 
dangerous condition. The available energy of the explosion 
was about 250,000,000 foot-pounds, and the damage produced 
was proportional to this enormous power. One boiler (No. 5) 
was thrown across the road and over a church ; the other (No. 
6) was thrown to one side, partially destroying neighboring 
buildings. The boiler-house was entirely destroyed. The third 
boiler remained unexploded, and was found a little out of place 
and nearly full of water. 



STEAM-BOILER EXPLOSIONS. 62/ 

According to the observer furnishing these particulars, the 
conclusions are inevitable: 

(•i) That the two boilers exploded in succession so quickly 
as to be practically simultaneous, beginning at the weak line 
AB of No. 6 boiler. 

(2) That they contained an ample supply of water. 

(3) That the pressure was too great for boilers of their size 
and condition. 

(4) That the use of cold feed-water hastened the deteriora- 




Fig. 171. — Piece of Patch. 

tion of poor iron, causing cracks and leaks, by which external 
corrosion was produced, and that the energy stored in the 
water of these boilers caused all the destruction observed. 

It is always to be strongly recommended that regular and* 
continuous feeding of hot water be practised ; and that the 
greatest care be exercised by inspectors and those in charge of 
steam-boilers in searching for and immediately repairing dan- 
gerous defects. 

The last figure is an excellent illustration of the appearance 
of iron when thus corroded and cracked. At C the crack was 
old, and partly filled up with lime-scale. 

The explosion of the upright tubular boiler is usually con- 
sequent upon some injury of its furnace, either by collapse 
or by the yielding of the tube-sheet to excessive pressure. 
The result is commonly the projection of the boiler upward 
like a rocket, and is rarely accompanied by much destruction 
of property laterally. A typical case of this kind is that of an 



628 



THE STEAM-BOILER. 



explosion occurring at Norwich, Connecticut, December "23, 
1 88 1, of which the following is a brief account : ^ 





^. 




,., 


^- - - — "^ "---^^ 




■' .---~'~-"^^ ' ~^/ 




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Fig. 172. — Explosion of an Upright Boiler. 

Fig. 253 represents the location of the boiler and engine 
immediately before the explosion. The explosion took place, 

as shown in figure; by the yielding 
of the lower tube-plate of the boiler. 
This boiler was three feet in diam- 
eter and seven feet high, and was 
four years old. The boiler was 
made of five-sixteenths iron through- 
out. It contained sixty tubes, two 
inches in diameter, five feet long, 
which were set with a Prosser ex- 
pander, and were beaded over as 
usual. The upper tube-head was 
flush with the top of the shell, and 
the lower, forming the crown of the 
furnace, was about two feet above 
the grates and the base of the shell, 
and was flanged upon the inner sur- 
face of the furnace. There was a 
safety-plug in the lower tube-head, 
which was not melted out, although, as is often the case when 

* Scientijic American, Jan. 14, 1882. 




Fig. 173.- 



-boiler-room before the 
Explosion. 






S TEAM-B OILER EXPL SIONS. 



629 



these plugs are so near the fire, a portion of the lower part of 
the fusible filling had disappeared. 

, The working pressure was sixty pounds per square inch, 
and the explosion probably took place at or a little below this 
pressure, throwing the boiler through the 
roof and high over a group of buildings, 
and a tall tree close by, finally burying 
itself half its diameter in the frozen ground. 
There had been leak in the tubes, and 
four had been plugged. There was a 
crack in the upper head near the centre, 
which extended between three tubes. 

From this crack steam escaped, and the water had settled upon 
the surrounding surface of the tube-head and the tube-ends. 
The result was to reduce the five-sixteenths plate to less than a 
quarter of an inch in thickness, and the tube-ends to the thick- 
ness of writing-paper. The lower tube-ends had suffered still 




Yielding Tube- 




Fig. 



-The Exploded Boiler. 



more from leaks, and were as thin as paper, and afforded no 
adequate support to the head. The pressure consequently 
forced the lower head down, opening fifty or more holes two 
inches diameter, from which the fluid contents of the boiler 
issued at a high velocity and the whole boiler became a great 
rocket, weighing about two thousand pounds. 



630 



THE STEAM-BOILER. 



One life was destroyed by this explosion and a considerable 
amount of property. 

An explosion which occurred at Jersey City, N. J., some 
years ago, illustrates at once the dangers of low-water and of 

a safety-valve rusted fast. As re- 
ported at the time,* " The boiler 
was of the locomotive type, having 
a dome upon the top. The en- 
^^^...^^^^^^^^^^finii: -iiiiimi^^ff gineer upon the morning of the ex- 
I '^^^^^^m/hJ^^M plosion lighted the fire in the boiler, 
Jl^^ffllliiir^^''^lillEs^ and shortly afterwards was called 

away, leaving the boiler in charge 
of his nephew, who was young and 
inexperienced in the handhng of 
steam. After putting fresh coal in 
the furnace he was called away by 
one of the owners of the dock to 
assist at some outside duty. Upon 
his return he saw the seams of the 
boiler opening, and attempted to 
open the furnace-door, but was un- 
able, owing to the excess of pressure of steam within the boiler 
which had caused the head to change its shape. A few mo- 
ments afterwards the explosion occurred, the firebox being 
thrown downwards, the top of the shell and crown-sheet up- 
wards, while the cylinder part shot directly up the street. It 
struck the ground about 400 feet from its original position, 
demolished a fire-hydrant, several trucks, trees, and a horse, and,, 
spinning end for end, came to rest by the side of a truck, which 
it destroyed, about 642 feet from its starting-point. Subse- 
quent investigation revealed the fact that the boiler was not 
properly supplied with water. A portion of the crown-sheet 
which we examined showed conclusively that near the fiues it 
was red-hot. We also examined the safety-valve, which was of 
the wing pattern, having a lever and weight. This valve was 
so firmly corroded to its seat that it could not be removed, and 




The Explosion. 



Am. Machinist, Oct. 



1881. 



STEAM-BOILER EXPLOSIONS. 



631 



the stem was also corroded fast. The whole secret of this ex- 
plosion is that the boiler was short of water, and an excessively 
high pressure of steam was raised to an unknown point, which, 
without relief, acquiring sufficient force, tore the boiler to 
pieces." 

The valve was found, and, being placed in a testing-ma- 
chine then under the charge of the Author, at the Stevens In- 
stitute of Technology, was only started by a pressure of a ton 
and a half, " while nearly two tons was required to move it 
observably. 

Change of form with varying pressures and temperatures 
sometimes produces most unexpected defects. It has been ob- 
served that many locomotive boilers 
stayed as in the figuref give way at 
the side, in the manner here exhib- 
ited. Investigation shows that in 
these cases the tying of the furnace- 
crowns to the shell by the system of 
staying illustrated, and the continual 
rising and falling of the furnace rel- 
atively to the shell, is very apt to 
cause a buckling of the outside sheet '= 
along the horizontal seam, which 
finally yields. This buckling and 
straightening of the sheet goes on ^^i^. i77.-Faulty Staying. 
until a crack or a furrow is formed along the lap nearest the most 
rigid brace, and, when this has cut deeply enough, the side of 
the boiler opens, often, the whole length of the furnace, the ex- 
plosion doing an amount of damage which is determined by the 
steam-pressure, the quantity of energy stored, and the extent 
of the rupture. 

In these cases, either the crown-bars over the furnace or the 
stays should alone have been used ; their use together is 
objectionable. Of the two systems, probably the first is the 
safer in such boilers. 




* Am. Machinist, Oct. 22, li 
f Locomotive, Jan. i, 18S0. 



632 



THE STEAM-BOILER. 



The appearance of a collapsed flue is seen in the two succeed- 
ing figures, which represent the results of experiments made by 
the U. S. Commission appointed to investigate the causes of 



/<J[ 


^^ 




B«^^ 




lii/^Wi 


H^^^H 






^^g 


11"°' '°llm.^^^^ " 




^H^pi 


^^ i ^^H^^ 


^& 



Fig. 178.— Collapsed Flues. 




179. — Collapsed Flues. 



explosions of steam-boilers. In neither case did the boiler 
move far from its original position. Collapsed flues rarely 
cause extensive destruction of property. 

The explosion of a rotary rag-boiler, receiving steam from 




Fig. 180. — An Exploded Boiler. 

steam-boilers at a distance, which took place at Paterson, N. J., 
wrecked the mill, destroyed a part of an adjacent establish- 
ment, and caused serious loss of life and property. The dis- 
aster was due to weakening of the boiler by corrosion, but, not- 
withstanding its reduced strength, the shock of the explosion 
was felt and was heard throughout the city, and heavy plate- 
glass windows were broken at a considerable distance from the 
scene of the accident. Explosions of this kind show the fallacy 



STEAM-BOILER EXPLOSIONS. 633 

of many of the absurd and mischievous '' theories" which have 
been prevalent in regard to explosions. 

Where the iron or steel used in the construction of the boiler 
is of good quality, strong, uniform, and ductile, the smaller torn 
parts of an exploded boiler may not break away from the main 
body; such a case is illustrated in the last figure (180), which 
represents the effect of an explosion of a new boiler from 
a cause not ascertained. The boiler was 15 feet long by 4 feet 
diameter, with 38 four-inch flues. Both heads remained on the 
flues, but the shell of the boiler burst along the rivet-holes 
nearly all around both heads, as shown in the engraving. 

294. Experimental Investigations of the causes and 
methods of steam-boiler explosions have been occasionally 
attempted. One of the earliest and most systematic, as well as 
fruitful, was that of a committee of the Franklin Institute, 
the results of which were reported to the Secretary of the U. S. 
Treasury early in 1836. 

This committee proposed by experiment-r- 

I. To ascertain whether, on relieving water heated to, or 
above, the boiling-point, from pressure, any commotion is pro- 
duced in the fluid. 

To determine the value of glass-gauges and gauge-cocks. 

The investigation of the question whether the elasticity of 
steam within a boiler may be increased by the projection of 
foam upon the heated sides, more than it is diminished by the 
opening made. 

II. To repeat the experiments of Klaproth on the con- 
version of water into steam by highly heated metal, and to 
make others, calculated to show whether, under any circum- 
stances, intensely heated metal can produce, suddenly, great 
quantities of highly elastic steam. 

To directly experiment in relation to the production of 
highly elastic steam in a boiler heated to high temperature. 

III. To ascertain whether intensely heated and unsaturated 
steam can, by the projection of water into it, produce highly 
elastic vapor. 

IV. When steam surcharged with heat is produced in a 



634 THE STEAM-BOILER. 

boiler, and is in contact with water, does it remain surcharged, 
or change its density and temperature ? 

V. To test, by experiment, the efficacy of plates, etc., of 
fusible metal, as a means of preventing the undue heating of a 
boiler or its contents. 

(i) Ordinary fusible plates and plugs. 

(2) Fusible metal, inclosed in tubes. 

(3) Tables of the fusing-points of certain alloys. 

VI. To repeat the experiments of Klaproth, etc. 

(i) Temperature of maximum vaporization of copper and 
iron under different circumstances. 

(2) The extension to practice, by the introduction of differ- 
ent quantities of water, under different circumstances of the 
metals. 

VII. To determine by actual experiment whether any per- 
manently elastic fluids are produced within a boiler when the 
metal becomes intensely heated. 

VIII. To obsexve accurately the sort of bursting produced 
by a gradual increase of pressure, within cylinders of iron and 
copper. 

IX. To repeat Perkins' experiment, and ascertain whether 
the repulsion stated by him to exist between the particles of 
intensely heated iron and steam be general, and to measure, if 
possible, the extent of this repulsion, with a view to determine 
the influence it may have on safety-valves. 

X. To ascertain whether cases may really occur when the 
safety-valve, loaded with a certain weight, remains stationary, 
while the confined steam acquires a higher elastic force than 
that which would, from calculation, appear necessary to over- 
come the weight of the valve. 

XI. To ascertain by experiment the effects of deposits in 
boilers. 

XII. Investigation of the relation of temperature and pres- 
sure of steam at ordinary working pressures. 

It is only necessary here to state that the results proved — 
(i) That relieving pressure even slightly produced great 
commotion in the water, and considerably relieving it caused 



STEAM-BOILER EXPLOSIONS. 635 

the violent ejection of water as well as steam through the open- 
ing by which the pressure was reduced. 

(,2) That under similar conditions pressure invariably dimin- 
ished. 

(3) That the injection of water upon the heated surfaces of 
the experimental boiler produced a sudden and considerable 
rise of pressure. 

(4) That the injection of water into superheated steam re- 
duced its pressure in all cases noted. 

(5) That superheated steam may remain in contact with 
water a long time (two hours in the experiments tried) without 
becoming saturated. 

(6) That fusible plugs, as then constructed, were unreliable, 
and the fusing-points of various alloys were determined. 

(7) That the temperature of maximum vaporization of w^ater 
is lowered by smoothness of surfaces ; that of iron is thirty or 
forty degrees higher than that of copper, while the time required 
is one half as great with copper ; that the temperature of maxi- 
mum vaporization, for oxidized iron, or for highly oxidized 
copper, is about 350° F., and that the repulsion between the 
metal and the water is perfect at from twenty to forty degrees 
above the temperature of maximum vaporization. 

(8) That no hydrogen was liberated by throwing water or 
steam upon heated surfaces of the boiler; that the water was 
not decomposed, and that air cannot occur in any appreciable 
quantity in a steam-boiler at work. 

(9) That " all tJie circiunstances attending the most violent 
explosions may occur without a sudden increase of pressure with- 
in a boiler,'' the explosion being produced by gradually accu- 
mulated pressure. 

(10) That but a small part of water, highly heated, can ex- 
pand into steam, if suddenly relieved of pressure. 

(11) That water can be heated to very high temperature 
only under intensely high pressure. 

(12) That steam-pressure may rise even after it has raised 
the safety-valve. 

Unpublished experiments recently made by Professor Mason 
at the Rensselaer Polytechnic Institute strongly confirm the so- 



636 



THE STEAM-BOILER 



called " geyser theory" of Messrs. Clark and Colburn. In these 
experiments a number of miniature boilers were constructed, 
and were exploded by a gradually produced excess of pressure, 
and in such manner as to test this theory. The first of these 
boilers, w^hen exploded, produced such an effect, blowing out 
windows and shaking down the ceiling of the laboratory as 
effectually to dispose of the idea prevalent among certain classes 
of engineers that a true explosion could only be caused by low- 
water and overheated plates. Another boiler was so set that, the 
rear end being lower than the, front, the quantity of water acting 
by percussion, according to the Clark theory, was much greater at 
the one end than at the other. The consequence was that 
while the one end was broken into many pieces, that in which 
there was least water was simply torn from the mass of the 
boiler and was itself unbroken. In one of this series of experi- 
ments the boiler was broken into more than a hundred pieces, 
although made of drawn brass — a material far less liable, ordi- 
narily, to be thus shattered than iron or steel. The second of 
the above-described experiments appears to the Author a very 
nearly crucial test and proof of the theory of Messrs. Clark and 
Colburn. 




Fig. 181. — Bomb-proof, 

In the work of investigation involving the explosion of 
steam-boilers it is usually necessary to provide a safe retreat for 
the observers, from which to watch the progress of the experi- 
ment, and from which to read the steam-gauge, to watch the 
water-level, and to take the readings of the thermometers or 
pyrometers. 



STEAM-BOILER EXPLOSIONS. 637 

The illustration represents the structure, composed of heavy 
timber, and partially underground, used at the testing-ground 
at Sandy Hook, by the U. S. Commission of 1873-6. 

These experiments were projected and conducted by Mr. 
Francis B. Stevens of Hoboken, and at the request of Mr. S. 
the United Railroad Companies of New Jersey appropriated 
the sum of ten thousand dollars to enable Mr. Stevens to enter 
upon a preliminary series of experiments. They at the same 
time invited other railroads and owners of steam-boilers to co- 
operate with them, and offered the use of their shops for any 
work that might be considered necessary or desirable during 
the progress of the work ; no such aid was, however, received. 

Several old boilers had recently been taken out of the 
steamers of the United Companies. These were subjected to 
hydrostatic pressure until rupture occurred, were repaired and 
again ruptured several times each, thus detecting and strength- 
ening their weakest spots, and finally leaving them much 
stronger than when taken from the boats. The points at which 
fracture occurred and the character of the break were noted 
carefully at each trial. 

After the weak spots had thus been felt out and strength- 
ened, the boilers were taken, with the permission of the War 
Department, to the United States reservation at Sandy Hook, 
at the entrance to New York harbor, and were there set up in 
a large inclosure which had been prepared to receive them, and 
the four old steamboat-boilers above referred to, together with 
five new boilers built for the occasion, were placed in their 
respective positions without having been in any way injured. 

Finally, on the 22d and 23d of November, the experiments 
to be described were made. 

The first boiler attacked was an ordinary " single return-flue 
boiler." 

The cylindrical portion of the shell was 6 feet 6 inches 
diameter, 20 feet 4 inches long, and of iron a full quarter inch 
thick. The total length of the boiler was 28 feet : the steam 
chimney was 4 feet diameter, loj- feet high, and its flue was 32 
inches diameter. The two furnaces were 7 feet long, with flat 
arches. There were ten lower flues, two of 16 and eight of 9 



638 



THE STEAM-BOILER. 



inches diameter, and all were 15 feet 9 inches long; there were 
twelve upper flues, 8J inches in diameter, and 22 feet long. 
The total grate-surface was 38I- square feet, heating-surface 
1350 square feet. The water-spaces were 4 inches wide, and 




Fig. 182.— Marine Boiler. 



the flat surfaces were stayed by screw stay-bolts at intervals of 
7 inches. The boiler was thirteen years old, and had been 
allowed 40 pounds pressure. 

The upper portion of the boiler, when inspected before the 
experiment, seemed to be in good order. The girth-seams 
on the under side of the cylindrical portion had given way, and 
had all been patched before it was taken out of the boat. The 
water-legs had been considerably corroded. 

In September this boiler had been subjected to hydrostatic 
pressure, giving way by the pulling through of stay-bolts at 66 
pounds per square inch. It was repaired, and afterward, at 
Sandy Hook, was tested without fracture to 82 pounds, and 
still later bore a steam-pressure of 60 pounds per square inch. 

On its final trial, November 22d, a heavy wood fire was built 
in the furnaces, the water standing 12 inches deep over the 
flues, and, when steam began to rise above 50 pounds, the 
whole party retired to the gauges, which were placed about 



STEAM-BOILER EXPLOSIONS. 



639 



250 feet from the inclosure. The notes of pressures and times 
were taken as follows : 



Time. 


Pressure. 


Time. 


Pressure. 


Time. 


Pressure. 


Time. 


Pressure. 


2.00 P.M. 
2.05 " 
2.10 " 


58 lbs. 
68 " 
78 " 


2.15 P.M. 
2.20 " 
2.23 " 


87 lbs. 
9ii " 
93 " 


2.25 P.M. 
2.30 " 
2.35 " 


9ii lbs. 
91 " 
9ii " 


2.40 P.M. 
2.45 " 
2.50 " 


9li lbs. 
91 " 
90 " 



The pressure rose rapidly until it reached about 90 pounds,* 
when leaks began to appear in all parts of the boiler; and at 93 
pounds a rent at {A, Fig. 182) the lower part of the steam- 
chimney where it joins the shell becoming quite considerable, 
and other leaks of less extent enlarging, the steam passed off 




Fig. 183. — Stayed Water-space. 



more rapidly than it was formed. The pressure then slowly 
diminishing, the workmen extinguished the fires by throwing 
earth upon them, and the experiment thus ended. 

The second experiment was made with a small boiler (Fig. 
183), which had been constructed to determine the probable 
strength of .the stayed surface of a marine boiler. It had the 
form of a square box, 6 feet long, 4 feet high, and 4 inches thick. 
Its sides were -f-^ inch thick, of the " best flange firebox" iron. 
The water-space was 3-| inches wide. The rivets along the 
edges were J inch diameter, spaced 2 inches apart. The two 



* The ultimate strength of this boiler, when new, was probably equal to about 
double this pressure. 



640 



THE STEAM BOILER. 



sides were held together by screw stay-bolts, spaced 8f and 9^^. 
inches, and their ends were slightly riveted over, precisely copy- 
ing the distribution and workmanship of a water-leg of an ordi- 
nary marine boiler. It had been tested to 138 pounds pressure.. 
This slab was set in brickwork, about five sixths of its capacity 
occupied by water, and fires built on both sides. Pressure 
rose as shown by the following extract from the note-book of 
the Author : 



Time. 


Pressure. 


Time. 


Pressure. 


Time. 


Pressure. 


Time. Pressure. 


3.18 P.M. lbs. 


3.28 P.M. 


20 lbs. 


3-37 P.M. 


54 lbs. 


3.46 P.M. 117 lbs. 


3-20 ' 


4 " 


3.29 " 


23 " 


3-38 " 


58 " 


3.47 " 126 " 


3-21 ' 


5 " 


3-30 " 


27 " 


3 39 " 


65 " 


3.48 " 135 " 


3-22 ' 


7 " 


3-31 " 


30 " 


3-40 " 


72 " 


3.49 " 147 " 


3-23 ' 


9 " 


3.32 " 


34 " 


3-41 " 


78 " 


3.50 " 160 " 


3- 24 ' 


i II " 


3 33 " 


38 " 


3.42 " 


86 " 


3-51 " 165 *' 


3-25 ' 


13 " 


3-34 " 


44 " 


3-43 " 


94 " 


Exploded. 


3.26 ' 


15 " 


3-35 " 


49 " 


3-44 " 


100 " 




3-27 ' 


18 " 


3.36 " 


51 " 


3-45 " 


no " 





At a pressure of sHghtly above 165, and probably at about 
167 pounds, a violent explosion took place. The brickwork of 
the furnace was thrown in every direction, a portion of it rising 
high in the air and falling among the spectators near the gauges • 
the sides of the exploded vessel were thrown in opposite direc- 
tions with immense force, one of them tearing down the high 
fence at one side of the inclosure, and falling at a considerable 
distance away in the adjacent field ; the other part struck one 
of the large boilers near it, cutting a large hole, and thence 
glanced off, falling a short distance beyond. 

Both sides were stretched very considerably, assuming a 
dished form of 8 or 9 inches depth, and all of the stay-bolts drew 
out of the sheets without fracture and without even stripping 
the thread of either the external or the internal screw : this 
effect was due partly to the great extension of the metal, which 
enlarged the holes, and partly to a rolling out of the metal as 
the bolts drew from their sockets in the sheet. 

Lines of uniform extension seemed to be indicated by a 
peculiar set of curved lines cutting the surface scale of oxide on 



STEAM-BOILER EXPLOSIONS. 



641 



the inner surface of each sheet, and resembhng closely the lines 
of magnetic force called by physicists magnetic spectra. 
These curious markings surrounded all of the stay-bolt holes. 

The third experiment took place at a later date. The 
boiler selected on this occasion was a " return-tubular boil- 
er" with no lower flues, the furnace and combustion-chamber 
occupying the whole -lower part. Its surface extended the 
whole width of the boiler, thus giving an immense crown-sheet.. 

This boiler was built in 1845, ^^^^ had been at work twenty- 
five ycaj's ; w^hen taken out, the inspector's certificate allowed 
30 pounds of steam. In September it was subjected to hydro- 
static pressure, which at 42 pounds broke a brace in the crown- 
sheets, and at 60 pounds 12 of the braces over the furnace gave 
way, and allowed so free an escape of water as to prevent the 
attainment of a higher pressure. The broken parts were care- 
fully repaired, and the boiler again tested at Sandy Hook to 59 
pounds, which was borne without injury, and afterward a steam- 
pressure of 45 pounds left it still uninjured. At the final ex- 
periment the water-level was raised to the height of 15 inches 
above the tubes, and it there remained to the end. The fire 
was built, as in the previous experiments, with as much wood as 
would burn freely in the furnace, and the record of pressures was 
as follows: 



Time. 



12.21 P.M. 
12.23 " 
12.25 " 



Pressure, 




Time. 



Presssure. 



12.32 P.M. 50 lbs., brace broke. 

12.33 " 52 " 

12.34 " 53i- " exploded. 



In these second and third experiments we have illustra- 
tions of the comparatively rare cases in which explosions 
actually occur. 

The second was a perfectly new construction, in which cor- 
rosion had not developed a point of great comparative weak- 
ness, and the edges yielding along the lines of riveting on all 
sides simultaneously and very equally, the tw^o halves were com- 
pletely separated, and thrown far apart with all of the energy of 
41 



642 THE STEAM-BOILER. 

unmistakable explosion, although there was an ample supply of 
water, and the pressure did not exceed that frequently reached in 
locomotives and on the western rivers, and although the boiler 
itself was quite diminutive. 

In the third experiment as in the second it is probable that 
the weakest part extended very uniformly over a large part of 
the boiler, either in Hues of weakened metal, or over surfaces 
largely acted upon by corrosion. Immediately upon the giving 
way of its braces, fracture took place at once in many different 
parts. 

295. Conclusions. — We may conclude, then, from the result 
of Mr. Stevens' experiments : 

First. That '' low-water," although undoubtedly one cause, 
is not the only cause of violent explosions, as is so commonly 
supposed ; but that a most violent explosion may occur with a 
boiler well supplied with water, and in which the steam-pressure 
is gradually and slowly accumulated. 

This was shown on a small scale by the experiments of the 
committee of the Franklin Institute above referred to. 

Second. That what is generally considered a moderate steam- 
pressure may produce the very violent explosion of a weak 
boiler, containing a large body of water, and having all its flues 
well covered. 

This had never before been directly proven by experiment. 

Third. That a steam-boiler may explode, under steam, at a 
pressure less than that which it had successfully withstood at 
the hydrostatic test. 

The last boiler had been tested to 59 pounds, and after- 
v/ard exploded at 53-J pounds. This fact, too, although fre- 
quently urged by some engineers, was generally disbelieved. 
It was here directly proven.* 

* A number of instances of this kind, though not always producing an explo- 
sion, have been made known to the Author. Two boilers at the Detroit Water 
Works, in 1859, after resisting the hydrostatic test of 200 pounds with water, at 
a temperature of 100° Fahr,, broke several braces each at no and 115 pounds 
steam-pressure respectively, when first tried under steam. The boiler of the U. 
S, steamer Algonquin was tested with 150 pounds cold-water pressure, and broke a 
brace at 100 pounds when tried with steam. A similar case occurred in New 
York a few years ago, and the boiler exploded with fatal results. These acci- 



II 



STEAM-BOILER EXPLOSIONS. 643 

In addition to the deductions summarized above, the 
Author would conclude — 

Fourth. That the violence of an explosion under gradually- 
accumulating pressures is determined largely by the nature of 
the injury and the extent of the primary rupture due to it. 
A merely local defect or failure would not be likely to cause 
explosion. 

Fifth. That the overheating of the metal of a boiler in con- 
sequence of low-water may or may not produce explosion, ac- 
cordingly as the sheet is more or less weakened or as the 
amount of steam made on the overflow of the dry heated area 
by water is greater or less. 

Sixth. That the superheating of either water or steam is 
not to be considered a probable cause of explosions. 

Seventh. That the question whether the repulsion of water 
from a plate by the overheating of the latter may occur with 
resulting explosion remains unsettled ; but that it is certain 
that the number of explosions attributable to this cause is 
comparatively small. 

Eighth. That all explosions are certainly due to simple and 
preventable causes, and nearly all to simple ignorance or care- 
lessness, on the part of either designer, constructor, proprietor, 
or attendants. 

A committee of the British House of Commons, after long 
study and careful investigation of this subject, made the fol- 
lowing recommendations : 

(a) That it be distinctly laid down by statute that the 
steam-user is responsible for the efficiency of his boilers and 
machinery, and for employing competent men to work them ; 
{b) that, in the event of an explosion, the onus of proof of 
efficiency should rest on the steam-user ; {c) that in order to 
rdlsQ priina-facie proof, it shall be sufficient to show that the 
boiler was at the time of the explosion under the management 
of the owner or user, or his servant, and such prima-facie 
proof shall only be rebutted by proof that the accident arose 

dents are probably caused by changes of form of the boiler, under varying tem- 
perature, which throw undue strain upon some one part, which may have already 
been nearly fractured. 



644 THE STEAM-BOILER. 

from some cause beyond the control of such owner or user ; 
and that it shall be no defence in an action by a servant against 
such owner or user being his master, that the damage arose 
from the negligence of a fellow-servant. 

Tlic Prevention of steam-boiler explosions is now seen to 
be a matter of the utmost simplicity. A well-designed, w^ell- 
made and set, and properly managed steam-boiler may be con- 
sidered as safe. Explosions never occur in such cases. To 
secure correct design and proportions, a competent engineer 
should be found to make the plans ; to obtain good construc- 
tion, a reliable, intelligent and experienced maker must be 
intrusted with the construction under proper supervision and \ 

precise instructions from the designer ; and the latter should 
also attend carefully to the installation of the boiler. In order 
to insure good management, trustworthy, skilful, and experi- 
enced attendants must be found, who, under definite instruc- 
tions, may at all times be depended upon to do their work 
properly. Periodical inspection, prompt repair of all defects 
when discovered, and the removal of the boiler before it has 
become generally deteriorated and unreliable are absolute safe-' 
guards against explosion. 



I 



APPENDIX. 



646 



O. o ^ HJ 
(U G (" S 



fin 

•§^-^^- 

<U rt 3i "J 

O rt ° tn 

a. w tn *^ 

^ !> b 3 

;2 ^ o rt 
^ t/: ^ a 

■u ^ - 



•2 3 m 






5 iJ 5 i; 



<1 rt 2 a (u 



J3 rt 



3 03 

cr-g 
■53 tfl ° "5 he 

lifll 



c 



OtJ-^ 9JJS 

- c/) G i> 
(/5 a! ^ . 



THE STEAM-BOILER. 



spunod ui 


•qoui ajBnbs aad 

'ttinnoBA B aAoqB ajnssajj 


a. 


H N ro ■* invo t^oo ON 


S-^? 


1' 


•ONO t^ 


\ 


S 

D 

> 


•Aiisuap uinuiixBui jo 
aanjBaadma; vz aajBAv p3|[ijsip 
JO iqSiaM ^Bnba jo amnjoA 
01 ra^ajs JO auin[OA jo oiib-jj 


^ 


vo t~^ m IT) 1000 ro O'^O ro 


ON lO w 
1- o-oo ?L 


1^, 

1 '^ 


NO m ■* 




t^iOTj-mrocs N (N 


Pt M M H 


1- 


M 1-. H 




•jaaj 
oiqna ui tnBa;s jo punod b jq 


^ 


M vo Ti- osiri t-v ro 
■<l-0\m>ou^Hoo« tvoo 


ScS-^=i?> 


ro 


lO .-ooo 
00 ro ON 




0"I^O^PlwMVOMt^ 
ro t-^ M 00 t^vo 10 -^ -"i- to 


;?;?^s^5- 


t 


lO ■* P) 




•spunod 
UI 'IUB31S JO looj oiqna b jo ^qSp^ 




ro lOOO M rovo 00 " rovo 
0000000000 


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1 


i 2? 


•i- 
00 










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it 
1 


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w 



s 

P 
2 

< 


•uouBJodHAa JO siTun ui ^zZ 
aAoqB uopBJodBAa jo jBaq pjox 


^ 


PI t- ro N t-^oo tv ^ C 
P) 0< '^oo w ro 10 r>. C3> M 
10 mvo vo tv. t^ t^ tv t>voo 


Tj- r>. ON H 
p< ro ^vo 
oooooooo 


! 


Ill 


*G 

a 

<u 
x; 
H 

1 

m 

G 


"o G 


tt; 


1 

lON-<»-MP)P)000ONPJ 

lOVO -^ -"l-VO -* ^00 

"*• 1-1 vo -^-oo o> t> rooo 


lO lOOO ON 
t-^ UO -*NO 

P4 in t^oo 


1 


ON o-oo 




ro 1000 H ro 10 (-^ ov 
1-1 p< P4 M rororororo-"!- 


HH 


NO 


NO t^OO 




Latent heat of 

evaporation 

at pressure P 

= I + E. 


^ 


^ a-co t-^ ON ^ ONO? ON ro 
ro rooo --t-vo tj-vo CN 


00 NO r-- 
o'm tQ 


i 


ro oco 


3 


ro'O lOt-sO lOOvo W ON 
OOOOOONONONONON 


NO ro t-- 

ON On ON ON 


NO 


On ON On 


X rtX! 


^ 


2'2'SKv§ O'^o'ovo 
\0 w ^ t^^D ^ VO H 10 


t-^ P) ro ro 


t^ 


Pi lOcS 


1 


^OVOVOVONOVOVOVO t-^i-^ 


t^ t^ t^ t^ 


t^ 


t^ t> t^ 


1 


1— 1 


^ 


VO >o t^ 0-00 ^ ro 'i- N 
OnOO N On ro ro lOOO 00 t-^ 
rOO-l^lOP) OMDOO lONO 

H I-' 6^6 ro t-^ H vd pj 00 

ONONONONONONONONONON 


o' "on ON 

ON ONOO 00 


00 


O^ONOO 


1 

J3 


Required to 

raise the 

temperature 

of the water 

from 32° to T°. 


^ 


000 -^M roH roioONO 


lO t-^ PJ P) 


!o 


NO ON 


* 


as;s^sg,%^m^NS 


NO -^00 
NO t-^ t-^ t^ 


% 


C^C^S 


•saaaSap 3iaqaajqB^ 'ajnjBjaduiax 


- 


w o>op) r^t^-<i-to 1000 
ro^ H ro H ON ON ro P) 1 


00 ONNO 


o 


O ro ^ 




P)\0 M rOP) OO NOO ro 
O W -* >OVO t^ t^OO 00 ON 


Sggg 


P) 


rONO On 








spun 


od UI 


•qoui ajBnbs jad 
'rannDBA b aAoqB aanssajj 


a,' 


M p) ro Tf lONO r^oo ON 


H N ro ^ 


On 
NO 


tONO t^ 





(I 



APPENDIX. 



647 



a, 


..8 


H (N f; ■* lONO t^oo ON 

NNN<N<NNN(NtNm 


H (N m Tj- inNO t-oo ON 
m m ro m m m co m m ^ 


H f) m ■5^ mvo t^oo On 


M p) m Th mvo tv 
m m m m m m m 


^* 


On N IH 
in ON ro 


Ti- rooo NO in m 


00 00 N Onoo 00 t^ m 


mmoNQ t^O t~-ONmm 


On t^OO PI On P) ' 

2 5 gvi JCn^nB 1 

m m -"S- Tj- Tj- ^ .^ 


vo CO 00 N 00 r~.oo M 

M^ ", 0__ 0_ ON ON o>oo 00 00 


::?5NNg^'=5-^^8NfCE;^^ 

00 t^ r^ t^ t^ r^NO NO NO NO 


t->moN^.rj-mM 6 6 


^ 


00 m 
t^ r^ t^ 


Tf-*0 M NOOOO MOO 
00 ro\0 rhoo ro ON -"j- 


t^oo Noovco t^ ON moo 
vo m onno m t^ m w 


Ocovo ^N Ooovo T^m, 


m t>- -s-NC ^No PI 

00 mj On m PI On t^ 
w 00 t-NO ^ m 


M ON 
N C» M 


00 00 t~-NO iO m rj- Tj- ro rri 


m<NP)MMHH666 


ON ON On ON 000 00 00 00 


00 03 t^ t>~ tv t^ t> 


„. . „„.. 




^ 


82^ 


T*-^ (N"Ti-ooininw 
i-^Tj-i- t^ci t^- T^r^o 

0^ o^^o "o "o "o ^ 00 


S |; S>nS S v£-n2;|;^ ^ 


->j- Tt- M mvo -^ On H t~v 
1- ONt^^i-iOO -^M t^pg 


H m PI 00 N ^ -"J- 
S ? N "S m m m 














^ 


522^ 

ON ON ON 


s:HsH&HI 


^ S =§ ^"2 ^'S ^^"^ ? 
? 8 8 8 8 8 8 8 8 S 


CO moo N NO Tj-00 « vo 

8 nils 8 811 


N_ PI P) P) N c^ p3 

i 


"■"" 




^ 


t>\o ^ 


m^D NHt^ONh-v-^wO 

NO «vo t^mwvDoo onoo 

N I^T|-«00 -^CO (N 


00 TfON^O mo ^ONTj- 


N o-NO ■* m ON'O vo 00 m 
CO Pivo Onm c-i mmpi m 
CO m i^ H vo T^oo pi vo 


m ONOO P) m M 
ONVO m NO - NO 


??,:?> 


p) ro rt- in in mo t- t-~oo 


oooNONOi-iM(NN(Nim 
m in inNO no no no no \o 


m T^ Tj- m mvo vo vo t-^ t^ 

VOVOVOVOVONOVOVOVOVO 


vo~Sno vo vo no^ r- 






















•-^ 


N N H 
t^ t^OO 


0^ 0) iOOO n" K 0? t^% 


r-» On f^ " t>.00 ->1- t^ N 


0000 moo 00 •* ■* 

^S;Sn5nS^5^^^ 


m -*NO t^ ON H m 
vo m -4- m pi p) H 

ON ON On ON ON ON ON 


OONO Tj- 

in in in 

ON o\ ON 


N w On t^\0 ^ m H ON 

ln^nTl-T^-T^^T^T^TJ-r^^ 

ONO-ONO-ONONQNONONCN 


t^NO in m N H Onoo t^ 
0- On ON O. On On On On On ON 


m -* m N H Onoo i-- 

OnOnOnOnOnOnOnOnOnOn 


^ 


03 in 


ON N NO m rooo t-~ H 00 On 
t-v ON H roinNOoo - ro 


NO ^0 '^^ o~ m S tC 5*0 
■*NO r~.Do M c( m T)-\o 


On r^ P) mNO m w m t^ t^ 

t-^00 On w P) m rj- mvo 


NO '^ -*vo t^vo 
ONOO t^ m m. M On 

vo 1^00 i-l M 


ro ro rr) 
t^ t> t~. 


rorOThTt-Tf-^Tt-ininu-) 


m in in inNo no no vo no no 


VOVOVO t^t^t-^l-.t-~t->lv. 


?^ Ei E^ [^'^'^'S. 


N 


H tv ON 


ON f~~oo 00 f^ N M m 


- H N moinON(N On<n 
(N rvmOND m, oooNO ti- 


w moo -<*• On m r^ On t^ m 
pj n Onoo f~. KS No'vo vo 


m P) f~-vo H 00 

vo tt t^CO ON w 


o-r~.inr^M Ooovo mm 
t^t-^r^c-^r^t^No>ONONO 
oooooooooooocooooooo 


cs ONOO NO in Tt- (N H 
NOVO inininininininm 
00000000000000000000 


ONOO vo'm^mcjHOON 

^Tj-^ThTj-Tj-TfTj-Tt-m 

oooooooooooocooooooo 


00 i^vo m ■* Tt- m 


Co 


00 CO in 

O" ONVO' 


in i>.oo r- ON m moo >-i 

00 1- lAMOOOO N OnQNO 
N00<NNO000lS<Nm(N 


in w f. ^vo M H VO 
vo IN CNl On H mvo -^oo 
M 000 inmovo MOO m 


M ONVO mo H 00 PJ ■* m 
ON moo N NO 5- tv m 


M- mvo M 00 m t^ 
P) t^ <M H On m 
\0 00 M m mvo 00 


H rONO 

On ON ON 


I8gll5 5;ss 




t^ ON c» m mvo t^ ON 
mmTt-Tf-^-.^Ti-Ti--*m 

PINNONNNNNN 


H p) -^ mvo t-.oo 

P) W C? N W N N 


- 


(N ino 

M- N On 


in o~ ON m m in m^o m m 


E-giSsssl^vS'^ 


PI t^ m t^ Tt-No 00 t-^ M- 
vo 1- m On m t-^ mNO on 


moo 00 00 m M m 
H mm t^ ONM N 


Hs 


o,^^f;^o ^^Nooo 

(N)(N(SNCSC^!NC^NP) 


N T)-inwON0 CNl -^int^ 
in in in in mvo vo vo vo vo 

CN)MP)(N(N«(N)W(N(N 


NO t-^t--t^t^i^t^t^ f^oo 

PJNCTPJPJNPIPIPJP) 


C» 00 CO OT^OOOOOO 


^ 


^2^§ 


H (s m Tj- in\o t^oo on 

N««MNNNP)(Nm 


w (N) m r^ mNO r^oo on 
mmmmmmmmm-^ 


H cj m ^ mvo t^oo ON 


H N m Ti- invo t^ 
m m mm m mm 



648 



THE STEAM-BOILER. 



spunod ui 


•tjoui ajBnbs jad 

'ranuDBA B aAoqB ajnssajj 


^ 


%^^ 


vSvSvS'vS-v^SvS^SvH"?. 


w <S ro T^ 100 

t^ t^ C^ tv t^ t^ 

1 


w 

s 


> 


■Aiisuap mnia.iXEOi jo 
ajmBjadoiaj ib aajBA\ panpsip 
jo jq.8iaAV i^nba jo auinioA 
0} coBais JO aranioA jo on^-jj 


^ 


t^ 10 lO 


i^NOOvoNOoowooinro 


ro T)-vo 10 M 


->!- Tf Tj- 


H'S-^l-IH'i;^ 


H^i^^ 


•laaj 
Diqne ui uiBais jo punod h jq 





t^ t^ r> 


■OMO-OLntNNTj- OvVO 

ONQO two IT) •* m cj M 
NO vd vd \d NO vo NO 


ON OOO r-No'vo 
ui lA IT) 10 10 10 


•spunod 
ui 'raB3js JO jooj oiqnD b jo iqSpAV 


^ 


<N 00 N 

lit 


1 

oncs u-ii-^o N ^10 r-,00 

1003 <N int^CNM foio 

t)-vO onh roi/-)r^o CN ^ 


i 

1 Tj- m p^ (s in 

1 t^ S 5-vo <» 
NO ON M CO 10 c^ 

1 NO NO t-~ tv t^ Cv 










% 



s 

H 

< 
D. 

a 


•uouBJodBAa JO siTun ni 'oz£ 
aAoqB uouBjodBAa jo inaq ibjox 


b 


f) (N S 


[.^ rONO roNO On N m 


00 M -^ t^ ro 

"->NO NO NO t^ P^ 
P) N « 5 N f) 














i2 

"5 
B 
- 

1 

n 




^ 


inoo i-i 


10 ON ONNO On r^ ro T^ M NO 

(N 'S-NO (.^00 ON On OnOO 
inoO M Tl- t^ r^.NO ON f) 


00 NO " 10 
p.xNo in m H 00 

moo - Ti- p^ ON 


H 
i-^ r^ p^ 


wMCNOfirorororOTj- 


S:s:tc;ct^K 














Latent heat of 

evaporation 

at pressure P 


^ 


lJ^ t-^ 0\ 


t^NO mo r-^mp-O N 0. 
LnONTfONO .*(N CN 0) 

H mvO ON - Tf t-- 0-)N0 


-^NO rooo fO 
ON NNO ON (N NO 


ON 


00 t-^>o Lo Lo .^ m fo (N M 

a§N8N8N8N8N8N8NSN8N 


nrsts 


lis 


^ 


^'l^ 


Tf xr_\o 0- t~^00 0- On w 


I'll %%% 


CO 00 00 

f^ t^ t^ 


0000000000000000 OnOn 


0^ 0> 0^ 0^ 0^ On 

t^ t^ t^ t^ r^ t^i 

1 


m 


s 


li» 


sI-JHHHr 


t>. ro moo M 


00 00 00 


00 00 00 00 00 00 00 00 00 00 


S S 8 2"2*i2 

00 CO 00 00 00 CO 


Required to 

raise the 

temperature 

of the water 

from 32° to T°. 


Co 


Ir? 


rO Tl- 10 lONO NO NO NO NO VO 


ro t^ fO t>. 
<n ON m ON oi in 
NO m m ^ ^ m 


\D >D vO 


m 1- iriNO t>-oo On H P< 

VONONONONCNONO f~.t^I-~ 
(NtS(N(NCN(NC>l(N<N(N 


ro T*. mNo p^co 
p.~ p.- t^ p^ t^ pv 


•saajSap jiaquajqHjj 'ajnjBjaduiax 


tm 


H^ 


m P^oo 10 CS ro M f^ .<• 
"". i-NO roT^'rmO r^ 
NO t-^ r-00 00 00 00 00 00 P^ 


HUH 


i^g^l 


S ON S^ 0^ ON 
(NNNNpjNNromro 


iu\n. 


spun 


3d UI 


•qoui ajBnbs jad 
'uinnoBA B aAoqB ajnssajj 


^ 


00 0' 


M N ro Tf lONO P>.00 ON C 
NONONONONONONONONO t^ 


M N m .* inNO 

t>. P> C^ t^ C>. PN. 



APPENDIX. 



649 



C^ t^'S. C^OO 000000000000000000 ON ONO>0\ONOvO\0.0\0>0 


SS?S-S'^^'§§^2 


H f) m Tj- mvo t^ 




^ ^ .- 




00 in 10 


NOoo H mONiOMOo u^T^ 




>n NO P) onno m M ONOO 


tvNO VO NOVO t>s00 

N P» P) N P) P) N 


^ 


NO M 00 ^ 
m ro ro m 




vo mo c^ ^ M onno m M 
ON ON ONOO 00 00 r^ t^ t~» t^ 


ooNO mwooNO T^P) ONt- 
NONONONO inininin-*^ 

NP<PJP)P)PIP)P)P)PJ 


^ 


inoo N 00 


M (N M w OnOO 00 t^ CvNO VONO lOlO-^Tj-rom 


SvS?c^^2?:%?Ng^ 

mNOHHHQOGON 


in pj 00 NO in in 
mo t^ m t~~ Tj- 
On ONOO 00 00 t^ t^ 


10 IT) .n 10 


10 10 m 10 in IT) ■*• ^ '^ ^j- ■* Tf -"i- Tf -^ ^ ^ ^ I*- Tf 


■*■<*■^■<J•-.J-Tl-■*T^•<J-m 


m m m f»i m m m 


^ 


t^ ON ON t^ 

00 CO 00 00 


rot^O w w " ONinom 
N M M ONOO NO in -J- N 
00 M -"fiOf^ONH- roin 

§2^2^S^S;8no^^| 


ONt^mroO t^ino On 
r^OO IN -^NO t^ On M N 
(N in t^ On M ro 1000 

MHMMP-.|NN(NNfO 

Nf)NCJ<N)«N(NP)p) 


■*NO 00 On H m -^NO t-- On 1 w P4 -^ in t~^00 

?^ ^^% ^ ;? 15! ^ 0: ;;, 1 ;?;^~^^^.£- 

NP)P)NP)P)P)PJP)P) p)P)PIOPJNN 










l:^ 


vo ON H T^ 

t^ r^oo 00 

P) 0) N N 


ooononononggoO" 
n(nn(ncnn(n)n«(s 


<NN(N(N(NnS(N(N<N 


NOOO PJ int^ONH Tj-NO 
mmTJ-T^T^T^TJ-lnlnln 

p)p»e)p)P)NPip)p)P) 


^vgvgvS-S-Sa 

P) P) P4 PJ P) P4 PI 
P4 N P) P) P) P) PI 






















t^ 


S;g^SN§ 


M tv M ro P) moo On 


OnIOOnm t- t^p) lONO 

-^tVM rl-I^ONN Tj-NO 

00 N in f^ ON M ThNO 00 


in m On m mNO no •* « no 


ON ON On ON ONOO CO 

w mm f- C3NM m 


^^^E^ 


t>. f^ C^OO 00 00 00 On On On 


t^oo oooooooocSooTOCo 


00 00 00 (» 00 00 00 co'm'oo 


■<i- TT -^ Th -^ in in 
00 00 00 00 00 00 00 


HHHH 











•"^ 


IHI 


0> t^ t^ t^OO On w t^No' On 
Tl-00 P)NO ^ONfOt^M 


r<Nt^c) r^Noo ION ONt-^ 
NO 10 On -*-oo rnoo P< t^ 


m t^NO on Tj- P) T^ Th 
inmpjMMMMpgm-*- 


m Tj- ONOO H t^ T^ 
NO 00 m t^ ^ 
p) t^ moo m. On -* 


HII 


ON ON On On O- ON ON O-OO 00 
00 00 00 00 00 00 00 00 00 00 


oooooocooooooooooooo 


mpjp<i-«00ON o-oo 1 00 rv t-^NO NO in in 
oooocooocooooo t^t-»r^ t^i-^t^t--i-^t-^t^ 

00000000000000000000 00000000000000 


^ 


NO N ON>0 
10 lANO NO 


OnNNO Onm n rompj 

^OinONO HVO HNO !^ 
t-^00 OOOnOnOOwi-iN 


in m On Thoo m t^ P) NO 
p) n ro ro Ti- Tun inNO no 


inONmt-^H. inoNmt^ 

t~^ f- t^OO 00 On On On O 


r^ ^ H t^ m 
M -^oo P) in On m 
M H M pg P» P) m 


On Ov On On 
f^ C-% t^ C~. 


g:?:s?:ScgcgcScgcg 


^cScg^cg^^cgcgcg 


cgc§^cg<g^<§^cScS 


00 00 00 00 00 00 00 


s 


00 t^ ro 

NO tN On M 

Tl- t^ -t- 


N t^ ONOO <N ^ N H NO 

T^t-~,wNo MOO inN 000 
t~^ ■5^ r-. " -^00 N NO On 


inoominOHin mco 
t- C-. p- i>.oo P) Tj- t^ 
ro C^ M U-) ON Tt-OO N NO M 


Tj-co moo m On m P) on S. 
in On -^00 m t^ P) (>. H NO 


m tv in tv Tj- Tf -^ 

HVO H VO H VO H 


t^NO no' \r, 


Ti-TtmN P) H 6 0' ONOO 


IHHcgl'HI' 


000000^ On'on'on 0^ 

0000000000 t^t^t^t^t^ 


t^vo VO in in ^ ^ 


00 00 00 00 


OOOOOOOOOOOOOOCOOOOO 


^ 


c. M q ON 


0i-iN->i-0NOt^0mro 


M ONt^mmoooNO mo 


IN NO m"*-M Tt-PJ -"j-M P) 


S^vgi'Svg^i 


?:!<«<» 


i~>:^i->:ifi 


s^g^lli^Hl^i^l 


"IH^^HH?! 


T%H\ll 


- 


N w CO 


t^iOThP) 000 t-«inroO 


t^ m PI m ONOO H ON m 
t-. in pj 00 moo m\o o pj 
00 NO Tj- H On NO ■* M ONNO 


^NgNg^^^vS^Ng 5,E^^<S 

mo r^^Moo inp4 ONin 


Pi ON in p) 00 in H 


g'S M M 


fO ■>!• lONO NO t^OO On 


6 w P) m m ^ inNo" no t^ 


oooNONOHl-(cammT^ 


in U-INC t-V t-^00 On 

m m m m m m m 
m m m m m m m 


m fo CO ro 


mrorocommfrirr-, n-, rn 


ti. 


t^OO On M M ro •+ lONO r^OO On 

t^ c^ r^oo 000000000000000000 on 


3nSnS^S;^^S^^Sn8 


5S??^^^<§g^2 ss^r;?^^ 







650 



THE STEAM-BOILER. 



•qoui 34Bnbs jad 
spanod ui 'uinrioEA b aAoqB aanssajj 


^ 


'SS^g 


M (N m Th mvo tvoo ON 

W(NNN(N«INP)Nfn 


H N (n ■* inNo t^oo 
en en en en en en en en 




! " "i 


M 

s 

►J 


> 


•ilisuap mnoiixBCu jo 
ajniBaaduiai 5b j31bm panjisip 
JO iqSpA\ iBtiba jo 3Ujn[6A 
01 uiBais JO acanjoA jo oub-jj 


t\ 


.-„ 


1 

m t^ rONO T*-oo IN NO 


1 
HNO M t^pjoo T^0| 


N N N 


NO Tf m H ONOO NO TT ro W 

(NNNMCNNtSMCMP) 


illssisi 


•533J 

oiqno UI CDBais jo punod b jq 


^ 


IT) lO'O 


00 (N moo N NO in 
NONo ininInTj-Tj--.j-^% 


NO pjoo inp) oni^'tI 


IT) ro re 


enenenenenenenenenen 


fomroromcnmro 


•spunod 
ut 'UIB91S JO jooj oiqnD b jo iqSp^ 


^ 


^oo_ 
N <M <N 


H M ONt^roONrorvQ H 

N^cgS^g^^'^^N^cS^ 

in r-^ On p) -"j-NO o) P) ■* 

t^ t^ f-OO 00 00 00 ON ON ON 
P)P)NNNNNP)P)P) 


^00 w Si on ro t^ 

M pj ro inNo t^ ON 
c^ONH mint^ONN 
OnOnOOOOOi- 
pi P) enen enen enen 










i 

a 


•uouBjodBAa JO siiun ui 'o^S 
aAoqB uopBaodBA9 jo jBaq ibjox 


ti 


p>. i-^ rv 

N N (N 


00 N ^No 00 C4 m m 

t-^00 00000000 OnOnOnOn 

S S S S ?! S S S S S 


HoSoHo 
PJP1P<P1«P)«« 








'5 

s 

1 

H 
1 

c 


Total heat of 
evaporation 
above 32° 


^ 


10 t^ 0- 


H (VI U-) t^oO P) -*NO 00 


00 NO -^ PI OnNO ^ ^' 
ON M romNO 00 Pi 


00 00 00 


nOnOnovono t-~t^fvt-~t^ 
COCOOOCOOOOOOOOOOOOO 


t-00 00 00 00 00 00 
oocoooooooooooco 








Latent heat of 
evaporation 
at pressure P 





in ONO 
<§nS>S- 


NO 00 p) ONOO H t-, invo 00 

NO M t^^PloO ^Onu-imS 


rowpjinOt^t^O 


00 00 00 


roroNPiMHOOOON 
00000000000000000000 


onqo 00 00 r^ t^No NO 

NONONONONONONCNO 


C c 4J 


^ 


NO ro ON 


n- On moo P) NO ON H N ■* 
^ in in inNO no no t^ t-~ t^ 


in t^oo w p) N H 

00 C» TO on SS 01 0^ 








00 00 00 


oooooooooooooooocooo 


oocoooooooooooco 


13 4-> 


s 


NO HNO 


inNO 00 H mNO On rn r^ H 
wNO H t^p) t~vPioo roON 


1 

00 rj-rrinONininON 
ino ino inH t-^m 
-j-O inMNO P) t^ro 


t^ t^ t-^ 


Pi H H ON ONOO 00 t-s 


t^ t^NONO in in ^ -* 
oooooocooooooooo 

1 


Required to 

raise the 

temperature 

of the water 

from 32° to T°. 


Co 


N H in 


p)NO ONpi inr--ooO M N 
inw l>■<^0NO p) ONinM 


ininc< ininp) Tj-ro 
p)p)PiwOONt-^in 
t-rooNinHNo woo 


d H « 


p) fo m -"^ in "-.NO NO r^oo 


'S S^S^g « S pi s' 


ro CO r<~. 


enenenenener-, enenenen 


enenenenenenene^. 


•saajSap ijaqusjqBjj 'ajniBjadraajL 




t-~ n- 


,5 8^'S%5-S^^>S 

NO mONinH t^cnoNinH 




en en er-. 


H N p) m rj- ■<*• in inNO t^ 
en en en en en en en en en en 


b«00 00 On H M 


spun 


•qoui 3JBnbs jad 
od UT 'oinnoBA b aAoqB ajnssajj 


a. 


^2^g 


V- N ro T^ inNO t^oo On 
p)PJNWNP)P)P)P)m 


H Pi PO ;^ 12^ t;;«> 









APPENDIX. 



651 



a. 





« N r<i ■* tnvo t>vOO a\ 


Nga^as 


2g?,5-^Nga<S§N8 

(NWPJPJPJPJPiPtPJro 


HH 


S. 8 a 8 5> 8 S, 8 ?> 8 

lONO NO C^ t^oo 00 ON ON 








^ 


.0 


t^-<l-N 0\t^inrOH OS 


On CONO 00 00 


intvnmooo oncoOoo 


1^00 •-< 00 


NO roNO T^NO « ono ^0 


•00 .- 

OvON 


\0 -<f r<^ M OnCO t^\0 ■* 
0> ON ON O^ 0>00 00 CO 00 00 


ro Tj- in t>. 
t^NO 10 -^ ■* 


;?;'S??^rg^^sg^ 


c< w inoo 
00 t^NO m 


-5:-^°;j;^^->MO 


^ -^ 1 ^ ■■ r ^ 1 " " 


^ 


<»^ 


as 000 00 00 ON M (N 

HMOOOOOOONON 


NO M (V-,00 NO 

00 ro ONNO in 


Ti-wNooo mONf^ONtnin 
inNO t^ ON p) in ON moo m 
>- ONoooo t^NONO in in 


in t~. P) p) 


f §:Ks2^HHi 


"" 


cororororocnmmw 


W (N (N N (N 












^ 


It 

cr: rr, 


^ rn\n t^oo 00 r^NO in ro 
r^ roNO ON (N 1000 w -* 
Thvo f^oo ON H PI en in« 
00 N ^vo O^w llp-i^f^ 
romrorocococnroroco 


Ig-OcgS 


N pi H oooNO mwoom 
Tj- mNO r^ tvoo On w 
NO 00 p) ^No 00 " ro m 
Tj- Tj- m in m m mNo no no 


-&■ inNO 

^ t^ On 1- 

m m inNO 
t^oo On 


lo-.HI^ofcgoo 

NO NO NO NO t^ t^ t^ t^OO 00 
JH Pi ro Ti- lONO t^OO On 










" 


MHHMHHHMMPi 


b 




ii-i\o 00 w ro T^vo 00 


NO H NO ^ 


t^ N •* mvD t^ t^ h. c^ 
« ro ^ inNO t^oo ON M 

P)P)P)P)P)PJNP)NP) 


NO ■* t^ 


t^ l>^ l>. t>.C» (»<» TO ON S 
PiPJP)PiP)pip*PINW 


























^ 


■* ul 


t^oo <N ro ^ t^oo 1.^ 


tS u M N ON 

"Rnno ?^ 


moo ON-piP)roroe)P4 


-*- ^ 
t-. c^ ro LO 


Ocooo "i-o inONO 
NO Tj- M c-v ro lONO t^NO 


c^ o>. 


^^g^%.^^^'^'^ 


(N Tf m t^oo 

ON ON ON ON ON 


fi 8 a falsi a 


ro t^ H rj- 


r^ ro inoo N ^no 00 
NNPIP1P<P1P)P1NW 




















^ 




H M -^ t-.VO t^ NO ■* 


pj ON m ro m 

ON CO On t-~lO 


NO P) 00 ro Onno w ro On in 


°^S^2g 


NONO COOP) TtN ONO 
T^ P) NO ro M Tl-00 NO 'i- ro 


0000 


sI'^ss^lH^ 


00 00 00 00 00 


00000000000000000000 


IHi 


roNO ONrot^M ino mO 
t-^NO m m Tt- -^ ro 'r p) p) 


^ 





g^^^^sf^l^s 


NO -* N ro P) 
- in tv t~.NO 
NO 00 PI 'i- 


00 "O lOVO 00 ("^ •-" 'J^ 


^N§C?0 


2<S§2^?<?8SNcgS 


cScS 


00000000000000000000 


p) N rn ro m 

GO 00000000 


r^^ m m 4 4 4 4 4 4 ^ 
000000000000000000 00 


woo 00 00 


NONONONONONONo ininin 
00000000000000000000 


s 


°l 


(N roCO NO NO t^ NO ^ lO 
■^ M 00 ^ ^ N H OnOO t-^ 

0^ H t-»mONioONO N 


ON ON ro M 

c< inoo T^ M 


NO >* N 00 rooo " 00 
o-c» 00 'on 8 inco (oco ^ 


O^OOM 
N row 


Tj-OO H ^TTTj-M 000 

ro ^ " rooo t^NO vo 




^(NNmwOOOOnOn 


t^ t^NO NO NO 

r^ t^ t^ t>. i-^ 




P) PJ ro in 

P< " ON 

r^ r^ t^NO 


00 00 t^NO NO NO Tl- -^ ro ro 

NONONONONONONONONONO 


Co 


Is 


lOH r^ooo mON-a-0 10 


N 00 OnNO 


MOO pjoo t^int-^t^ro 
■*NO inO inr-0 rot^ro 
M •- t^ ro On rONO On 


^^^SSi, 


^Noo QNOOONO roo 
1-1 N in -*oo 00 NO ro ro 


cn en 


rorororocorororo fO co 


rn fo m ^S 


00 WNO rot^O Tt-c^O 


NO ONci ro 


H5ilH^B>l 


- 


N 00 
N CJ 


OwooNMONOONt^ro 
00 ro t^ N NO n-iNO On N 
"-, ON^O lO«NO MVO (N 


NO NO NO M NO 
ro P) 00 f^No' 


ON^ m m ro inoo O w 
in ro t^oo 00 r^ 10 Ti- 10 r>. 
t--t^iO(N00 rot-^O N ro 


NO N P) P^ 

ON ONNO T^ 


inoo NO H NO 00 NO rooo 


ro ro ^ tn iDNO 'O hv t^oo 


moo P) t~- M 

NO NO t^ f^OO 


inONrot^O Tj-t^H Th^, 


M T)-NO t~~ 

ro Tf lONO 


t-^NO in ^ P) ONNO ro NO 


^ 


^% 


^ ^ ? ^ :?^ 5:°5. ? 


NgacggNg 


2 8^5-S>n8^^8n8 

WWP«C<C<P<CJMP)rO 


S>82)8 

ro^ rfin 


5,8a8S,8S,8a8 

lONo NO f^ t-»oo 00 ON ON 









652 



THE STEAM-BOILER. 



The column headed " V in the table of the properties of 
saturated steam is useful for reducing the performance of differ- 
ent boilers to a common standard — this standard being that 
most generally accepted by engineers : the equivalent evapora- 
tion at atmospheric pressure and the temperature of boiHng 
water, or, as it is frequently called, the evaporation from and at 
212°. In the table it is assumed that the temperature of the 
feed-water is 32°, and an auxiliary table is added, giving 
corrections for any temperature of feed from 32° to 212°. 



CORRECTION FOR TOTAL HEAT IN UNITS OF EVAPORATION. 



Tempera- 


c 


Tempera- 


1 


Tempera- 


c 


Tempera- 


c 


Tempera- 


c 


ture of 


_o 


ture of 


ture of 





ture of 


.2 


ture of 





feed, Fah- 


y 


feed, Fah- 


^ 


feed, Fah- 


^ 


feed, Fah- 


1 


feed, Fah- 


1 


renheit 


V, 


renheit 


u 


renheit 


fc 


renheit 


renheit 


degrees. 





degrees. 


c3 


degrees. 






degrees. 




u 


degrees. 


3 


33 


.0010 


69 


0383 


105 


.0756 


141 


.1129 


177 


• 1504 


34 


.0021 


70 


0393 


106 


.0766 


142 


.1140 


178 


• 1514 


35 


.0031 


71 


0404 


107 


.0777 


143 


.1150 


179 


■ 1525 


36 


.0041 


72 


0414 


108 


.0787 


144 


.1160 


180 


•1535 


37 


.0052 


73 


0424 


109 


.0797 


145 


.1171 


181 


.1545 
•155^ 


38 


.0062 


74 


0435 


no 


.0808 


146 


.1181 


182 


39 


.0073 


75 


0445 


III 


.0818 


147 


.1192 


183 


.1566 


40 


.0083 


76 


0450 


112 


.0829 


148 


.1202 


184 


• 1577 


41 


.0093 


77 


0466 


113 


.0839 


149 


.1213 


185 


• 1587 


42 


.0104 


78 


0476 


114 


.0849 


150 


.1223 


186 


.1598 


43 


.0114 


79 


0487 


115 


.0860 


151 


•1233 


187 


.1608 


44 


.0124 


80 


0497 


116 


.0870 


152 


.1244 


188 


.t6i8 


45 


•0135 


81 


0507 


117 


.0880 


153 


.1254 


189 


.1629 


46 


.0145 


82 


0518 


118 


.0891 


154 


.1264 


190 


.1639 


47 


.0155 


83 


0528 


119 


.0901 


155 


•1275 


191 


.1650 


48 


.0166 


84 


0538 


120 


.0911 


156 


.1285 


192 


.1660 


49 


.0176 


85 


0549 


121 


.0922 


157 


.T296 


193 


.1670 


50 


.0186 


86 


0559 


122 


.0932 


158 


. 1306 


194 


.1681 


51 


.0197 


87 


0569 


123 


•0943 


159 


.1316 


195 


.1691 


52 


.0207 


88 


0580 


124 


•0953 


160 


•1327 


196 


.1702 


53 


.0217 


89 


0590 


125 


.0963 


161 


•1337 


197 


.1712 


54 


.0228 


90 


0601 


126 


.0974 


162 


.1348 


198 


•1723 


55 


.0238 


91 


061 1 


127 


.0984 


163 


• 1358 


199 


•1733 


56 


.0248 


92 


0621 


128 


.0994 


164 


.1368 


200 


•1743 


SI 


.0259 


93 


0632 


129 


.1005 


165 


.1379 


201 


•1754 


58 


.0269 


94 


0642 


130 


.1015 


166 


.1389 


202 


.1764 


59 


.0279 


95 


0652 


131 


.1025 


167 


.1400 


203 


•1775 


60 


.0290 


96 


0663 


132 


.1036 


168 


.1410 


204 


•1785 


61 


.0300 


97 


0673 


133 


.1046 


169 


.1420 


205 


.1796 


62 


.0311 


98 


0683 


^34 


• 1057 


170 


•1431 


206 


.1806 


63 


.0321 


9Q 


0694 


135 


.1067 


171 


.1441 


207 


.1817 


64 


•0331 


100 


0704 


136 


.1077 


172 


•1452 


208 


.1827 


65 


.0342 


lOI 


0714 


137 


.1088 


173 


.1462 


209 


.1837 


66 


.0352 


102 


0725 


138 


.1098 


174 


•1473 


210 


.1848 


(^1 


.0362 


103 


0735 


139 


.1109 


175 


.1483 


211 


.1858 


68 


.0372 


104 


0746 


140 


.1119 


176 


•1493 


212 


.1869 



APPENDIX. 



653 



TABLE \a. 

TEMPERATURES AND PRESSURES, SATURATED STEAM. 
IN METRIC MEASURES AND FROM REGNAULT. 





Steam-pressure. 


3 

a 


Steahi-pressure. 


a 

e 

OJ 


In Centimetres. 


In Atmospheres 


In Centimetres. 


In Atmospheres 


H 






H 






- 32° c. 


0.0320 


. 0004 


+ 14° c. 


I . 1908 


0.016 


31 


0.0352 


0.0005 


15 


1.2699 


0.017 


30 


0.0386 


0.0005 


16 


1.3536 


0.018 


29 


0.0424 


. 0006 


17 


I. 4421 


0.019 


28 


0.0464 


. 0006 


18 


1-5357 


0.020 


27 


0.0508 


0.0007 


19 


1.6346 


0.022 


26 


0.0555 


0.0007 


20 


I -7391 


0.023 


25 


0.0605 


0.0008 


21 


1.8495 


0.024 


24 


0.0660 


. 0009 


22 


1.9659 


0.026 


23 


0.0719 


0.0009 


23 


2.0888 


0.028 


22 


0.0783 


O.OOIO 


24 


2.2184 


0.029 


21 


0.0853 


O.OOII 


25 


2.3550 


0.031 


20 


0.0927 


0.0012 


26 


2.4988 


0.033 


19 


0.1008 


0.0013 


27 


2.5505 


0.034 


18 


0.1095 


0.0014 


28 


2.8101 


0.037 


17 


0. 1189 


0.0015 


29 


2.9782 


0.039 


16 


0.1290 


0.0017 


30 


3.1548 


0.042 


15 


0.1400 


0.0018 


31 


3.3406 


0.044 


14 


O.I518 


0.0020 


32 


3-5359 


0.047 


13 


0.1646 


0.0022 


33 


3-74II 


0.049 


12 


O.17S3 


0.0024 


34 


3-9565 


0.052 


II 


0.1933 


0.0025 


35 


4.1827 


0.055 


10 


0.2093 


0.0027 


36 


4.4201 


0.058 


9 


0.2267 


0.0030 


37 


4.6691 


0.061 


8 


0.2455 


0.0032 


38 


4 -9302 


0.065 


7 


0.2658 


0.0035 


39 


5.2039 


0.068 


6 


0.2876 


0.0038 


.40 


5.4906 


0.072 


5 


0.31 13 


0.0041 


41 


5-7910 


0.076 


4 


0.3368 


0.0044 


42 


6.1055 


0.080 


3 


0.3644 


0.0048 


43 


6.4346 


0.085 


2 


0.3941 


0.0052 


44 


6.7790 


0.089 


I 


0.4263 


0.0056 


45 


7.1391 


0.094 





. 4600 


0.0061 


46 


7-5158 


0.099 


+ 1 


0.4940 


0.0065 


47 


7.9093 


0.104 


2 


0.5302 


0.0070 


48 


8.3204 


0.109 


3 


0.5687 


0.0073 


49 


8.7499 


0. 115 


4 


0.6097 


0.0080 


50 


9.1982 


O.I2I 


5 


0.6534 


0.0086 


51 


9.6661 


0.127 


6 


0.6998 


0.0092 


52 


10.1543 


0.134 


7 


0.7492 


0.0199 


53 


10.6636 


0.140 


8 


0.8017 


0.0107 


54 


II. 1945 


0.147 


9 


0.8574 


O.OII 


55 


11.7478 


0.155 


10 


0.9165 


0.012 


56 


12.3244 


0.163 


II 


0.9792 


0.013 


57 


12.9251 


0.170 


12 


1.0457 


0.014 


58 


13-5505 


0.178 


13 


I.II62 


0.015 


59 


14.2015 


0.187 



654 



THE STEAM-BOILER. 



TABLE la. — Continued. 





Steam-pressure. 


t 

a 


Steam-pressure. 




In Centimetres, 


In Atmospheres 


In Centimetres. 


In Atmospheres 


+ 60° c. 


14.8791 


0.196 


+iio°C. 


I07-537 


1. 415 


61 


15.5839 


0.205 


Ill 


I I I. 209 


1.463 


62 


16.3170 


0.215 


112 


114-983 


I. 513 


63 


17.0791 


0.225 


113 


118. 861 


1.564 


64 


17.8714 


0.235 


114 


122.847 


i.6r6 


65 


18.6945 


0.246 


115 


126.941 


1.670 


66 


19.5496 


0.257 


116 


131-147 


1.726 


67 


20.4376 


0.267 


117 


135.466 


1.782 


68 


21.3596 


0.281 


118 


139-902 


1. 841 


69 


22.3165 


0.294 


119 


144-455 


1. 901 


70 


23-3093 


0.306 


120 


149.128 


1.962 


71 


24 -3393 


0.320 


121 


153-925 


2.025 


72 


25 4073 


0.334 


122 


158.847 


2.091 


73 


26 5147 


0.349 


123 


163.896 


2.157 


74 


27.6624 


0.364 


124 


169.076 


2.225 


75 


28.8517 


0.380 


125 


174-388 


2.295 


76 


30.0S38 


0.396 


126 


179-835 


2.366 


77 


31.3600 


0.414 


127 


185.420 


2.430 


78 


32.6811 


0.430 


128 


191. 147 


2.515 


79 


34-0488 


0.448 


129 


197.015 


2.592 


80 


35-4643 


0.466 


130 


203.028 


2 .671 


81 


36.9287 


0.486 


131 


209. 194 


2.753 


82 


38.4435 


0.506 


132 


215.503 


2.836 . 


83 


40 OIOI 


0.526 


133 


221.969 


2.921 


84 


41 .6298 


0.548 


134 


228.592 


3.008 


85 


43-3041 


0.570 


135 


235.373 


3.097 


86 


45 0344 


0.593 


136 


242.316 


3.188 


87 


46.8221 


0.616 


137 


249.423 


3.282 


88 


48.6687 


0.640 


138 


256.700 


3.378 


89 


50.5759 


0.665 


139 


264.144 


3.476 


90 


52.5450 


0.691 


140 


271.763 


3.576 


91 


54.5778 


0.719 


141 


279-557 


3.678 


92 


56.6757 


0.746 


142 


287.530 


3.783 


93 


58.8406 


0.774 


143 


295.686 


3.890 


94 


61.0740 


0.804 


144 


304.026 


4.000 


95 


63.3778 


0.834 


145 


312.555 


4.1T3 


96 


65 -7535 


0.865 


146 


321.274 


4.227 


97 


68.2029 


0.897 


147 


330.187 


4.344 


98 


70.7280 


0.931 


148 


339-298 


4.464 


99 


73 3305 


0.965 


149 


348.609 


4.587 


100 


76 000 


1,000 


150 


358.123 


4-712 


TOI 


76.7590 


1.036 


151 


367-843 


4.840 


102 


81.6010 


1.074 


152 


377-774 


4.971 


103 


84.5280 


I. 112 


153 


387.918 


5.104 


104 


87.5410 


I. 152 


154 


398.277 


5.240 


105 


90 6410 


I -193 


155 


408.856 


5-380 


106 


93-8310 


I 235 


156 


419.659 


5-522 


107 


97,1140 


1.278 


157 


430.688 


5-667 


108 


100 4910 


1-322 


158 


441-945 


5-815 


109 


103 965 


1.368 : 


159 


453436 


5.966 



APPENDIX. 



655 



TABLE \a. — Continued. 



3 


Steam-pressure. 


I 


Steam-pressure. 


a 


In Centimetres. 


In Atmospheres 


In Centimetres. 


In Atmospheres 


-hi6o°C. 


465.162 


6.120 


+196° c 


1074.595 


14.139 


161 


477.128 


6.278 


197 


1097.500 


14.441 


162 


489-336 


6.439 


I9S 


II20.9S2 


14.749 


163 


501.791 


6.603 


199 


1144.746 


15.062 


164 


514-497 


6.770 


200 


I168.S96 


15-380 


165 


527.454 


6.940 


201 


1193.437 


15.703 


166 


540.669 


7. 114 


202 


1218.369 


16.031 


167 


554.143 


7.291 


203 


1243.700 


16.364 


168 


567.882 


7-472 


204 


1269.430 


16.703 


169 


581.890 


7-656 


205 


1295.566 


17.047 


170 


596.166 


7-844 


206 


1322. 112 


17.396 


171 


610.719 


8.036 


207 


1349.075 


17.751 


172 


625.548 


8.231 


208 


1376.453 


18. Ill 


173 


640.660 


8.430 


209 


1404.252 


18.477 


174 


656.055 


8.632 


210 


1432.480 


18.848 


175 


671.743 


8.839 


211 


I46I. 132 


19.226 


176 


687.722 


9.049 


212 


1490.222 


19.608 


177 


703-997 


9-263 


213 


1519.748 


19.997 


178 


720.572 


9.481 


214 


1549-717 


20.391 


179 


737-452 


9-703 


215 


1580.133 


20.791 


180 


754-639 


9.929 


216 


1610.994 


21.197 


181 


772.137 


10.150 


217 


1642.315 


21.690 


182 


789.952 


10.394 


218 


1674.090 


22.027 


183. 


808.084 


10.633 


219 


1706.329 


22.452 


184 


826.540 


10.876 


220 


1739.036 


22.882 


185 


845-323 


II. 123 


221 


1772.213 


23-319 


186 


864.435 


11.374 


222 


1805.864 


23.761 


187 


883.882 


11.630 


223 


1839-994 


24.210 


188 


903 . 668 


11.885 


224 


1874-607 


24.666 


189 


923.795 


12.155 


225 


1909.704 


25.128 


190 


944.270 


12.425 


226 


1945.292 


25-596 


191 


965-093 


12.699 


227 


1981.376 


26.071 


192 


986.271 


12.977 


228 


2017.961 


26.552 


193 


1007 . 804 


13.261 


229 


2055.048 


27.040 


194 


1029.701 


13-549 


230 


2092 . 640 


27-535 


195 


1051.963 


13.842 









656 



THE STEAM-BOILER. 



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INDEX. 



A 

SEC. PAGE 

Air, minimum, required in Fire, . '. . . . . -77 178 

Anthracite Coals, . . . . . , , . .64 155 

Apparatus, forms of gas-analysis . , . , . . 265 531 

Applications of Boilers . . '. . . . . . 14 20 

Appurtenances of Steam Boilers, 10 18 

Area of Cooling Surfaces, formulas f6r, . , . , .98 221 



B 

Barrel Calorimeters, forms of, . . . . . . . 260 519 

use of, . 260 519 

Bituminous Coals, . . . ... . . .65 156 

Bodies, molecular constitution of, . . . . • . 109 241 

Boiler, common proportions and Work of, . . . . . 161 335 

conditions of efficiency of, . . . . . . 149 303 

design of Plain Cylinder, . . . , . . . 169 350 

determination of Value of, . . . , . . 246 485 

form and Location of Bridge-wall of, . . . . 179 381 

forming bent parts of, ... . . . . 190 403 

general decay of, . . . ' . . . . . 288 604 

management of, . . , , , . . 206 440 

local decay of, . . . . , , . . . 288 604 

matters of detail of, . . . . . . . 168 346 

number of, . . , . . ... . 164 340 

office of the Steam, . . . ' . . . . . i i 

operation of, . . . . . . , . . 212 445 

parts of, defined, . . . . . . . . 168 346 

selection of Type and location of, . . . . . 147 300 

size of, . . . . ' . . ' . . . . 164 340 

the Locomotive, . ". ' . ... . . 16 26 

transfer of Heat in the Steam', .' . . . .97 220 

The older Types of, . ' . ' . . . . . 3 4 

The Scotch, . . '. \ ', ', ''.•'. . 19 32 

Upright and portable. ' . ' . ' . ' . ' . . '.~"l'75 369 

Boiler-construction, controlling ideas' in, ' . ' ^. ^'^^'-^-- - ; • ^ ; ' 151 307 



66o 



INDEX. 













SEC. 


PAGE 


Boiler-Design, details of the problem of, . . . , . i66 


345 


general consideration of, 










. 167 


34^ 


principles of, . . 










. 150 


304 


problem stated, . 










. 164 


340 


special conditions affecting. 










. 156 


317 


Boiler-Power, 










. 164 


340 


Boiler-pressure, choice of, . 










. 149 


303 


Boiler-trials, errors of, ... 










. 262 


521 


precautions observed at, . 










• 257 


5T4 


purposes of, . 










. 244 


484 


record-blanks for. . 










. 257 


514- 


records of, . . . 










. 262 


521 


Boilers, appurtenances of Steam, 










10 


18 


assembling of, ... 










194 


42a 


classification- of, . 










II 


19 


common " Shell " stationary, 










. 15 


21 


corrosion of, . 










. 287 


601 


cost of, 










. 152 


311 


covering of, . 










. 178 


380 


coverings of, . 










. 227 


456 


cylindrical Tubular, 










. 171 


358 


defects of construction of, 










. 286 


596 


design of, 










285 


593 


deterioration of, . 










. 57 


144 


developed weakness of, . 










287 


601 


drawings of construction of, . 










186 


400 


efficiency of 










152 


311 


efficiency of the Steam, . 










234 


472 


energy stored in, . 










269 


541 


factors of safety for. 










152 


311 


general care of, . 










222 


454 


general instructions in managemer 


It of, 








. 233 


469 


Horse-power of, . 










145 


292 


inspection of, . 










195 


420 


inspection and test of, ... 








5 


5, 232 


140, 466 


management of, .... 










291 


612 


Marine Flue, . . . . , 










172 


361 


Marine ; older-forms. . 










17 


29 


Marine Sectional, .... 










21 


38 


Marine Tubular, .... 










173 


362 


Marine Water-tube, 










18 


30 


Methods of construction of, . 










186 


400 


corrosion in, . , 










289 


606 


decay in, . 










289 


606 


of locomotives .... 










177 


377 


periods of introduction of. 








• 


22 


39 



INDEX. 



66 i 



Boilers, power of, ... 

problems in the use of, . 

processes of construction of, 

relative security of, 

relative strength of Shell and Sectional 

relative value of, . 

repairs of, . . , 

sectional, . . 

Sectional and Water-tube, 

setting of, . . . 

special forms of, . 

shells of, . . . 

specification for Steam, . 

stationary Flue, , . 

staying in, . : . . 

Steam, explosions of, . 

suspension of, . 

testing Steam, 

transportation and delivery. 
Braced and Stayed Surfaces, 

Brass. . 

Bridge-wall of Boiler, Form and location of. 
Bursting, . . , . , . . 



C 

Calorimeters, Theory of, . 
Calorimetry, , . . . . 

Calking and chipping, . ... 

Charcoal, . ...... 

Chemical characteristics oi Iron, 
Chimney Draught, . , , . 
Forms of, , . , . , 
Flues, and Grate, relative areas of, 
size of. , . . . . 

Chipping and Calking, 

Coal Calorimeter, The, . . 

defined, . , . . 

Coals, anthracite, , . , . 

Bituminous, ... 
Coke, . . c . . . . 

Colburn's Theory of Explosions, 
Combustion defined ; Perfect combustion, 
efficiency of, . 
method of, . , 
rate of, . . . 
temperature of products of, 



SEC. 


PAGE 


144 


291 


25 


43 


186 


400 


284 


592 


58 


148 


250 


488 


231 


465 


20 


33 


174 


364 


177 


369 


23 


42 


55 


129 


202 


427 


170 


354 


192 


413 


268 


538 


177 


377 


196 


422 


198 


424 


60 


151 


54 


127 


179 


381 


271 


549 


261 


521 


92 


214 


193 


417 


70 


162 


30 


57 


157 


317 


158 


322 


160 


334 


158 


322 


193 


417 


263 


524 


63 


153 


64 


155 


65 


156 


69 


160 


275 


559 


62 


152 


236 


473 


148 


302 


79 


184 


78 


179 



662 



INDEX. 



Commercial efficiency, 

theory of, 
Conclusions relating to explosions, 
Construction of Boilers, defective, 
Construction, problem in Design and, 
Continuous Calorimeters, The^ 

Contract, 

purpose of Specification and. 
Cooling Surfaces, Area of. Formulas for, 
Copper, . . . . . 
Corrosion, chemistry of, . . 

method of, 

methods of, in Boilers, 

of Boilers, . 
Critical Point, .... 
Crystallization and Granulation, . 
Curves of Energy, 
Cylindrical Tubular Boilers, 



SEC. 


PAGE 


240 


474 


242 


477 


295 


642 


286 


59^ 


24 


43 


263 


524 


200 


426 


199 


425 


98 


221 


54- 


127 


223 


454 


224 


455 


289 


606 


287 


601 


129 


265 


37 


9a 


143 


289 


171 


35& 



Dampers, location and Form of, . , , , , , iSl 381 

Decay, general, of Boilers, ..,,,,, 288 604 

local, of Boilers, 288 604 

Methods of, in Boilers, ... . . = . . . 289 606 

Delivery of Boilers, . . . . . . . . . 198 424 

Deposits, Incrustation and effect of 99 2i8' 

Design and construction, problems in, . , . . . .24 43 

of Boilers, special conditions affecting, .... 156 317 

defects of, 285 593. 

Designing Boilers, principles involved in, . . . . . 6 11 

Deterioration of Boilers, 57 144 

Donny and Dufour, experiments of, 281 578 

Draught Gauges, 267 535 

natural and forced, ....... 155 314 

Drilling and punching, 189 402 

Ductility, 29 56 

of Metal, loss of, 59 149- 



Economy, relation of Area of Heating Surface to. 

Efficiency and Quantity of Steam, 

as indicated by Gas-analysis, 
combined power and .... 



252 


490 


163 


33& 


216 


449 


253 


48^ 



INDEX, 



663 



Eflficiency, commercial, .... 
finance of, . 

measures of, ... . 
of Boiler, conditions of, 
of Heating surfaces, Formulas for. 
Theory of commercial, 
Efficiency, variations of, with consumption of Fuel and size of 

grate, .... 
Efficiencies, algebraic Theory of. 

Elasticity 

Emergencies, 

Energetics; Heat-energy and Molecular Velocity, 

Energy, curves of, 

Heat and Mechanical, . 
Heat as a form of, . 
of Steam alone, . . c . 
stored, in Steam, .... 
stored, in Boilers, . . . . 
heated Metal, 
superheated Water , 
Evaporation, factors of, ... . 

usual rate of ^ . 
Excess of Pressure, ..... 
Expansion, Latent Heat of, ... 

Experimental explosions and investigations, 
Experiments of Donny and Dufour, . 

Leidenfrost and Boutigny, . 
Explosions, absurd, causes of, 
causes of, . 
Colburn's Theory of 
definition of, 
description of, . 
examples of, . 
experimental, . 
fulminating, 
improbable causes of, 
? Lavvson's and others 

methods of, . . 
of Steam-boilers, 
possible causes of, 
probable causes of, 
results of, . 
statistics of causes of. 
Theories of, 
usual causes of, 



experiments of, 



272 



SEC. 


PAGE 


240 


474 


239 


474 


235 


473 


149 


303 


98 


221 


242 


471 


251 


488 


241 


476 


29 


56 


229 


450, 462 


lOI 


233 


143 


289 


105 


237 


98 


221 


270 


548 


142 


285 


269 


541 


277 


567 


281 


578 


139 


278 


162 


338 


221 


454 


113 


243 


294 


633 


281 


578 


282 


583 


272 


550 


293 


550, 616 


275 


559 


271 


549 


271 


549 


293 


616 


294 


633 


271 


549 


272 


550 


276 


561 


274 


558 


268 


538 


272 


550 


272 


550 


293 


6i6 


273 


559 


274 


558 


272 


550 



664 INDEX, 

F 

SEC. PAGE 

Feed apparatus, 184 392 

Filtration, . ......... .124 260 

Fitting, . 188 402 

Fire, minimum air required in, ....... 77 178 

temperature of, 76 172 

Fire-rooms, closed and open, . . . . . . . 214 448 

Fire-tubes, . 153 312 

Fires, starting of, ........ . 207 441 

the management of, , . . 208 442 

Flanging and Pressing, ........ 189 402 

Flue-boilers, Marine, 172 361 

stationary, ........ 170 354 

Flues, Chimney and Grate, relative areas of, , . . . 160 334 

collapsed, .......... 271 549 

disposition of 180 381 

flanged and corrugated, - 61 151 

setting of 192 413 

Forced Draught, 213 448 

Forces and Work, computation of External, . . . .118 248 

Internal, . . . .118 248 

Form, effect of variation of, ....... 32 64 

Forms of Boilers, modern standard, I2 20 

Fuel, adaptation of, 88 206 

choice of 148 302 

economy of, ........ 81, 249 187, 487 

pulverized, .......... 71 164 

test of Value of 245 485 

use of various kinds of, ...... . 209 444 

Fuels, 63 153 

analysis of, 248 486 

artificial, 74 168 

commercial value of, 86 201 

composition of, 83 192 

efficiency of, 249 487 

evaporative Power of 247 485 

Gaseous 73 167 

heating effects of, ........ 84 194 

heating-power of, 75 169 

liquid, .......... 72 165 

and Gaseous 210 444 

solid, 211 445 

Furnace, adaptation of, 88 206 

and grate, ......... 159 329 

efficiency of, ........ 80 185 

management, 87 204 



INDEX, 



665 



Fusible Plugs, . . . . . 
Fusion and Vaporization, latent heats of, 



Galvanic Action, 

Gas-analysis, efficiency as indicated by, 
Gases, analysis of, 

defined: the perfect gas, 
Gaseous Fuels, 
Gauges, draught, . . 

Granulation and Crystallization, 
Grate and Furnace, 

Flues, Chimney, relative areas of, 
Grooving and furrowing. 



H 
Heat, as a form of energy, . 

and matter; Specific heat, 

and mechanical Energy, . 

conduction of , . 

convection of, . 

efficiency of Transfer of, . 

methods of Production of, 

nature of, . . . . 

production, transfer, and strength of 

quantities of, . . . . . 

radiation of, ... . 

Sensible and Latent, . 

Specific, . . , . . 

transfer of, ..... 

in Steam Boilers, . 

Transformations, . . 

utilization of, . . 
Heat-energy, as related to Temperature, 
distribution of, - . . 
quantitative measure of, 
Heaters, . . . 
Heating effects of Fuels, 
power of Fuels, 
Heating- surface to economy, relation of area of, 

efficiency of, Formulas for 
Heats, computation of Latent and Total, 

specific, of Steam and Water, . 

Total and Latent; Internal Pressures 

Helical Seams, 

Horse-power of Boilers, ..... 



and 



Work 



SEC. 


PAGE 


185 


393 


114 


214 


229 


462 


266 


535 


265 


531 


no 


241 


73 


167 


267 


535 


37 


90 


159 


227 


160 


334 


289 


606 


100 


229 


III 


242 


105 


237 


95 


217 


96 


219 


237 


473 


90 


208 


89 


207 


7 


12 


91 


210 


94 


216 


112 


243 


91 


210 


93 


215 


97 


:^j2,i^ (^ 


105 


237 


88 


15 


102 


235 


115 


244 


103 


236 


184 


382 


84 


194 


75 


169 


252 


489 


98 


221 


138 


276 


137 


275 


133 


271 


49 


117 


145 


292 



666 



INDEX^ 



I 



Improvement in Boilers, method and limit of, 
Incrustation, .... 
Incrustation and Deposits, effect of. 

Sediment, 
Inspections and Test of Boilers, . 
Inspector, duties of the, 
Internal Pressures and Work; Total and Latent 

computation of, 
Investigations and Experimental explosions, . 
Iron, Cast and Malleableized, 

choice of, for various parts, 

preservation of, 

Physical and Chemical characteristics of, 
specification of quality of, . 
Iron and Steel compared, . . 

durability of, . ... 
method of Test of. 



Heats^ 



SEC. 

5 
230 

99 
280 

56 
205 
133 
134 
294 

54 
44 

226 
50 
43 
3'& 

225 

41 



PAGE 

10 

462 

228 

574 
140 
438 
271 
271 

633 
127 
112 
564 

57 
108 

92 

457 
98 



Latent and sensible heat, 112 

Heat of Expansion, 113 

Heats, computation of, 138 

of Fusion and Vaporization, . . , . .114 

Lawson's and others' Experiments, 276 

Leakage, 228 

Leidenfrost's and Boutigny's Experiments, . . . . 282 

Lignites, . . . . . . . . , . .66 

Liquid Fuels, . . .72 

Liquids defined no 

Location and Type of Boiler, Selection of, . . . . 147 

Locomotive Boiler, The, . . . . . . . .16 

Boilers, 176 

Low-water, . . . . , 218 

causes of, 279 

consequences of, ....... 279 



M 

Marine Boilers, older Forms, 

Flue Boilers, . 

Tubular Boilers, 

Water- tube Boilers, 
Materials required, Quantity of, 
Metal, heated, energy stored in, 

loss of Strength and Ductility of, 



17 
172 

173 

18 

27 

277 

59 



243 
243 
276 

244 

561 
461 
583 
158 
165 
241 
300 
26 
371 
450 
568 
568 



29 
361 
362 
30 
45 
567 
149 



INDEX, 



667 



Methods of Explosions, 
Method of Treatment, effept of,„ 
Minor accessories, 
Mixed applications of Boilers, 

Types of Boilers, 
Molecular constitution of Bodies, 



Net efficiency, ,. , . • • 

Number of Boilers, , . . . . , 

O , 

Operation of Boilers, safety in, . . , , . , . g 

Overstrain, method of detecting, . . , . . . 35 



SEC. 


PAGE 


274 


558 


33 


70 


185 


393 


14 


20 


13 


20 


109 


241 


238 


473 


164 


340 



Paints and Preservatives, . 
Peat or Turf, .... 
Physical characteristics of Iron, 

State of Water, changes of, 
Pipes, Steam and Water, . 
Plain Cylinder Boiler, design of, 
Planing, ..... 
Plant, efficiency of a given, 
Plate, Grades and Quantities of Iron in Boilers, 

manufacture of Iron and Steel, 
Plates, drilled, ... 

punched. 
Portable Boilers, 
Power and efficiency, combined, 
of Boilers, 

Steam Boilers, 
Precautions, 

Preservatives and Paints, . 
Pressing and Flanging, 
Pressure, computation of Internal Work and, 

excess of, 

in Boiler, choice of, 

steady rise of, 
Pressures, control of Steam, 

relations of. 
Priming. , ... 

Principles of Boiler-Design, 
Problem of Boiler-Design, details of the, 
Production of Heat, methods of, 



227 


458 


67 


159 


30 


57 


128 


265 


182 


383 


169 


350 


188 


402 


243 


481 


39 


94 


40 


96 


50 


123 


50 


123 


175 


369 


253 


489 


175 


369 


144 


291 


292 


614 


227 


458 


189 


402 


134 


271 


221 


454 


149 


303 


283 


589 


215 


449 


136 


273 


219 


451 


150 


304 


166 


345 


90 


208 



668 



INDEX. 



SEC. PAGE 

Products of Combustion, temperature of 78 179 

Pulverized Fuel, . . . , * 71 164 

Punching and Drilling, . . . . . , . .189 402 

Q 

Quality of Metal, specifications of, , , . , , . 204 436 

Quantities of Heat, ....,,.., 91 210 

R 

Rate of Combustion, . , ,. 79 184 

Records for Boiler-trials, . . , , . , . .257 514 

Regnault's researches and methods, ...... 140 280 

tables, . . . . . . . . .141 281 

Resilience, . 29 56 

Riveting and riveting machines, 191 404 

Rivet-iron and Steel, rivets and, 47 114 

Rivets and rivet-iron and Steel, 47 114 

forms of, ......... 48 115 

Rivets, sizes of, ......... 48 115 

strength of, 48 115 

Riveting, Steam and Hand, . . . . . • .51 125 

S 

Safety Valves, 183 385 

Sample specifications, 203 421 

Scotch Boilers, . . .19 32 

Sea-water; deposits and remedies, . . . , . . 123 256 

Seams: fractured, . . . 220 453 

Helical, 49 117 

strength of riveted, 49 117 

Welded, 52 127 

Sectional Boilers, . . . . sees. 20, 154, 197; pp. 35, 314, 423 

and Water- tube Boilers, 174 364 

Security of Boilers, relative, 284 592 

Sediment, 230 462 

and Incrustation, . , 280 574 

Sensible and Latent Heat, , , 112 243 

Setting, contact with, . . . . # . . . 228 461 

Shapes, " Struck-up" or Pressed, 53 127 

Shearing, 188 402 

Shell and Sectional Boilers, relative strength of, . . .58 148 

Shell Boilers, 154 314 

common stationary, . . ... . .15 2t 

Shells of Boilers, 55 129 



INDEX. 



669 



Size of Boiler, 

Sizes of Tube, standard, 

Sdlid Fuels, 

Solids defined, . . . . ' 
Solution of Problems, general methods of, 
Spacing of Tubes, . . 
Specific Volumes of Steam and Water, 
Specifications and contract, purpose of, 

generally, form of, 
Spheroidal State, .... 

of Water, 
Standard Boilers, Marine, 

Forms of Boiler, development of, 

modern 

method, instructions and Rules for, 
Stayed and Braced Surfaces, 
Staying in Boilers, 
Steam alone, energy of, 

gauges, . . . • 

generation and application. 

getting up of, . 

stored energy in; Tables, . 

superheating, 

quantity of, . . . 

and efficiency, 
and Water pipes, 

specific Heats of, . 
volumes of. 
Steam Boilers, Powers of, . . 
Steam- Pressures, control of. 
Steel, characteristics of. 
Steel, choice of, for various parts, 
special precautions in using, 
specification of quality of. 
Rivets and rivet-iron and, 
and Iron compared, 

durability of, 
method of Test of. 
Stopping suddenly. 
Stored energy in Steam; Tables, 
Strength of Metal, loss of, 

principles relating to, 
Stress, margin of. 
Surfaces, Stayed and Braced, 



SEC. 


PAGE 


164 


340 


165 


341 


211 


445 


IIO 


241 


26 


43 


165 


341 


135 


272 


199 


425 


201 


427 


130 


268 


282 


583 


21 


38 


2 


2 


12 


20 


256 


491 


60 


151 


192 


413 


270 


548 


185 


393 


119 


252 


207 


441 


142 


285 


131 


269 


259 


517 


163 


338 


182 


383 


137 


275 


135 


272 


144 


291 


215 


449 


31 


63 


44 


112 


46 


"3 


43 


108 


47 


114 


38 


92 


225 


457 


41 


98 


219 


9 


142 


285 


59 


149 


28 


45 


34 


74 


60 


151 



670 INDEX. 

T 

SEC. PAGE 

Technical uses of Water, . . . , , , . . 124 260 

Temperature, differences of, . . . • • , . 290 609 

effects of, 36 83 

Heat energy as related to 102 235 

of Fire, .76 172 

of products of combustion, . , . , .78 179 

Temperatures, 91 210 

relations of, . . 136 273 

Tenacity, ... . 29 56 

Test, apparatus and Method of, 254 489 

of Boilers, inspection and, 56 140 

of Iron and Steel, method of, , . , . . .41 98 

Tests of Metal, specification of, . 204 436 

results of, . . . 42 , 104 

Test-trials, results of, . 258 504 

Standard, ....,.,.. 255 491 

Theory of Calorimeters, 261 521 

explosions, Colburn's, ...... 275 559 

Theories of explosions, 274 558 

Thermal and Thermodynamic relation, ..... 132 270 

Thermodynamic relation, Thermal and, ..... 132 270 

Thermodynamics, 116 245 

defined, 106 238 

first law of, ...... . 107 239 

second law of, 108 240 

application of, . . . •117 247 

Thermometry, . .92 214 

Time, effect of, . . . . . . . , . .34 74 

Total Heats, computation of, . . . , , . , 138 276 

Transfer of Heat, efficiency of, ..... . 237 473 

Transportation of Boilers, 198 424 

Tubes, leaky, . . . . . . . . . . 220 453 

setting of, . 192 413 

standard sizes of, . 165 341 

spacing of, . . 165 341 

Tubular Marine Boilers, . 173 362 

Type and Location of Boiler, selection of, .... 147 300 

Types of Boilers, mixed, ....,,,. 13 20 

special purposes and modern, , . . 4 7 

Upright Boilers, . . . , . • ; , . 175 369 



INDEX. 



67 



Value of Boilers, determination of, 
Valves, deranged safety, 
Vaporization, ..... 

Latent Heats of Fusion and. 
Variation of Form, effect of, 
Volumes, relations of, ... 



W 



Water analysis, 

and Steam pipes, 

Specific Heats of, 

changes of Physical states of, . 

composition and chemistry of, 

de-aeration, .... 

low, causes of, 

consequences of. 

Physical characteristics of, 

properties of; Water as a Solvent, 

purification of, ... 

sources and purity of "fresh," 

specific Volumes of Steam and, 

Spheroidal State of, 

superheated, .... 
energy stored in. 

Technical uses of, . 
Water-supply, regulation of. 

Water-tubes, 

and Sectional Boilers, 
Weather waste of fuel, 
Weakness, developed, of Boilers, 

Welded Seams, 

Welding, 

Wood, ...... 

Work, internal pressure and, 
Working iron, method of, . . . 



SEC. 


PAGE 


246 


485 


221 


454 


131 


269 


114 


244 


32 


64 


136 


273 


125 


261 


182 


383 


137 


275 


128 


265 


121 


254 


281 


578 


279 


568 


279 


568 


127 


263 


120 


253 


126 


262 


122 


255 


135 


272 


282 


583 


130 


268 


281 


578 


124 


260 


216 


449 


153 


314 


174 


364 


82 


191 


287 


601 


52 


127 


191 


404 


68 


159 


133 


271 


45 


113 



r 



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ELEMENTS OF ANALYTICAL MECHANICS. By Col. 

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IRON CO.'S POCKET-BOOK (THE). Containing many 
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TOPOGRAPHICAL DRAWING- AND SKETCHING. 

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THE WORKS OP JOHN RUSKIN. 

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FIELD ENGINEERING. A HANDBOOK of the Theory and 
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A TREATISE UPON CABLE OR ROPE TRACTION, 

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A METHOD OP CALCULATING THE CUBIC CdST- 
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THE FIELD PRACTICE OF LAYING OUT CIRCU- 
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THE DESIGNING OF ORDINARY IROi^ HIGHWAY 
BRIDGES. A new Practical Work, with many Tables and 
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A PRIMARY GEOMETRY. With simple and practical ex- 
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GENERAL PROBLEMS IN THE LINEAR PERSPEC 
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2 50 



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